Doc/api/concrete.tex

\chapter{Concrete Objects Layer \label{concrete}}


The functions in this chapter are specific to certain Python object
types.  Passing them an object of the wrong type is not a good idea;
if you receive an object from a Python program and you are not sure
that it has the right type, you must perform a type check first;
for example, to check that an object is a dictionary, use
\cfunction{PyDict_Check()}.  The chapter is structured like the
``family tree'' of Python object types.

\warning{While the functions described in this chapter carefully check
the type of the objects which are passed in, many of them do not check
for \NULL{} being passed instead of a valid object.  Allowing \NULL{}
to be passed in can cause memory access violations and immediate
termination of the interpreter.}


\section{Fundamental Objects \label{fundamental}}

This section describes Python type objects and the singleton object
\code{None}.


\subsection{Type Objects \label{typeObjects}}

\obindex{type}
\begin{ctypedesc}{PyTypeObject}
  The C structure of the objects used to describe built-in types.
\end{ctypedesc}

\begin{cvardesc}{PyObject*}{PyType_Type}
  This is the type object for type objects; it is the same object as
  \code{types.TypeType} in the Python layer.
  \withsubitem{(in module types)}{\ttindex{TypeType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyType_Check}{PyObject *o}
  Returns true if the object \var{o} is a type object, including
  instances of types derived from the standard type object.  Returns
  false in all other cases.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyType_CheckExact}{PyObject *o}
  Returns true if the object \var{o} is a type object, but not a
  subtype of the standard type object.  Returns false in all other
  cases.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyType_HasFeature}{PyObject *o, int feature}
  Returns true if the type object \var{o} sets the feature
  \var{feature}.  Type features are denoted by single bit flags.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyType_IS_GC}{PyObject *o}
  Return true if the type object includes support for the cycle
  detector; this tests the type flag \constant{Py_TPFLAGS_HAVE_GC}.
  \versionadded{2.0}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyType_IsSubtype}{PyTypeObject *a, PyTypeObject *b}
  Returns true if \var{a} is a subtype of \var{b}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyType_GenericAlloc}{PyTypeObject *type,
                                                  int nitems}
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyType_GenericNew}{PyTypeObject *type,
                                            PyObject *args, PyObject *kwds}
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyType_Ready}{PyTypeObject *type}
  Finalize a type object.  This should be called on all type objects
  to finish their initialization.  This function is responsible for
  adding inherited slots from a type's base class.  Returns \code{0}
  on success, or returns \code{-1} and sets an exception on error.
  \versionadded{2.2}
\end{cfuncdesc}


\subsection{The None Object \label{noneObject}}

\obindex{None@\texttt{None}}
Note that the \ctype{PyTypeObject} for \code{None} is not directly
exposed in the Python/C API.  Since \code{None} is a singleton,
testing for object identity (using \samp{==} in C) is sufficient.
There is no \cfunction{PyNone_Check()} function for the same reason.

\begin{cvardesc}{PyObject*}{Py_None}
  The Python \code{None} object, denoting lack of value.  This object
  has no methods.  It needs to be treated just like any other object
  with respect to reference counts.
\end{cvardesc}


\section{Numeric Objects \label{numericObjects}}

\obindex{numeric}


\subsection{Plain Integer Objects \label{intObjects}}

\obindex{integer}
\begin{ctypedesc}{PyIntObject}
  This subtype of \ctype{PyObject} represents a Python integer
  object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyInt_Type}
  This instance of \ctype{PyTypeObject} represents the Python plain
  integer type.  This is the same object as \code{types.IntType}.
  \withsubitem{(in modules types)}{\ttindex{IntType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyInt_Check}{PyObject* o}
  Returns true if \var{o} is of type \cdata{PyInt_Type} or a subtype
  of \cdata{PyInt_Type}.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyInt_CheckExact}{PyObject* o}
  Returns true if \var{o} is of type \cdata{PyInt_Type}, but not a
  subtype of \cdata{PyInt_Type}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyInt_FromLong}{long ival}
  Creates a new integer object with a value of \var{ival}.

  The current implementation keeps an array of integer objects for all
  integers between \code{-1} and \code{100}, when you create an int in
  that range you actually just get back a reference to the existing
  object. So it should be possible to change the value of \code{1}.  I
  suspect the behaviour of Python in this case is undefined. :-)
\end{cfuncdesc}

\begin{cfuncdesc}{long}{PyInt_AsLong}{PyObject *io}
  Will first attempt to cast the object to a \ctype{PyIntObject}, if
  it is not already one, and then return its value.
\end{cfuncdesc}

\begin{cfuncdesc}{long}{PyInt_AS_LONG}{PyObject *io}
  Returns the value of the object \var{io}.  No error checking is
  performed.
\end{cfuncdesc}

\begin{cfuncdesc}{long}{PyInt_GetMax}{}
  Returns the system's idea of the largest integer it can handle
  (\constant{LONG_MAX}\ttindex{LONG_MAX}, as defined in the system
  header files).
\end{cfuncdesc}


\subsection{Long Integer Objects \label{longObjects}}

\obindex{long integer}
\begin{ctypedesc}{PyLongObject}
  This subtype of \ctype{PyObject} represents a Python long integer
  object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyLong_Type}
  This instance of \ctype{PyTypeObject} represents the Python long
  integer type.  This is the same object as \code{types.LongType}.
  \withsubitem{(in modules types)}{\ttindex{LongType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyLong_Check}{PyObject *p}
  Returns true if its argument is a \ctype{PyLongObject} or a subtype
  of \ctype{PyLongObject}.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyLong_CheckExact}{PyObject *p}
  Returns true if its argument is a \ctype{PyLongObject}, but not a
  subtype of \ctype{PyLongObject}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyLong_FromLong}{long v}
  Returns a new \ctype{PyLongObject} object from \var{v}, or \NULL{}
  on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyLong_FromUnsignedLong}{unsigned long v}
  Returns a new \ctype{PyLongObject} object from a C \ctype{unsigned
  long}, or \NULL{} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyLong_FromLongLong}{long long v}
  Returns a new \ctype{PyLongObject} object from a C \ctype{long long},
  or \NULL{} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyLong_FromUnsignedLongLong}{unsigned long long v}
  Returns a new \ctype{PyLongObject} object from a C \ctype{unsigned
  long long}, or \NULL{} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyLong_FromDouble}{double v}
  Returns a new \ctype{PyLongObject} object from the integer part of
  \var{v}, or \NULL{} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyLong_FromString}{char *str, char **pend,
                                                int base}
  Return a new \ctype{PyLongObject} based on the string value in
  \var{str}, which is interpreted according to the radix in
  \var{base}.  If \var{pend} is non-\NULL, \code{*\var{pend}} will
  point to the first character in \var{str} which follows the
  representation of the number.  If \var{base} is \code{0}, the radix
  will be determined base on the leading characters of \var{str}: if
  \var{str} starts with \code{'0x'} or \code{'0X'}, radix 16 will be
  used; if \var{str} starts with \code{'0'}, radix 8 will be used;
  otherwise radix 10 will be used.  If \var{base} is not \code{0}, it
  must be between \code{2} and \code{36}, inclusive.  Leading spaces
  are ignored.  If there are no digits, \exception{ValueError} will be
  raised.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyLong_FromUnicode}{Py_UNICODE *u,
                                                 int length, int base}
  Convert a sequence of Unicode digits to a Python long integer
  value.  The first parameter, \var{u}, points to the first character
  of the Unicode string, \var{length} gives the number of characters,
  and \var{base} is the radix for the conversion.  The radix must be
  in the range [2, 36]; if it is out of range, \exception{ValueError}
  will be raised.
  \versionadded{1.6}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyLong_FromVoidPtr}{void *p}
  Create a Python integer or long integer from the pointer \var{p}.
  The pointer value can be retrieved from the resulting value using
  \cfunction{PyLong_AsVoidPtr()}.
  \versionadded{1.5.2}
\end{cfuncdesc}

\begin{cfuncdesc}{long}{PyLong_AsLong}{PyObject *pylong}
  Returns a C \ctype{long} representation of the contents of
  \var{pylong}.  If \var{pylong} is greater than
  \constant{LONG_MAX}\ttindex{LONG_MAX}, an \exception{OverflowError}
  is raised.
  \withsubitem{(built-in exception)}{\ttindex{OverflowError}}
\end{cfuncdesc}

\begin{cfuncdesc}{unsigned long}{PyLong_AsUnsignedLong}{PyObject *pylong}
  Returns a C \ctype{unsigned long} representation of the contents of
  \var{pylong}.  If \var{pylong} is greater than
  \constant{ULONG_MAX}\ttindex{ULONG_MAX}, an
  \exception{OverflowError} is raised.
  \withsubitem{(built-in exception)}{\ttindex{OverflowError}}
\end{cfuncdesc}

\begin{cfuncdesc}{long long}{PyLong_AsLongLong}{PyObject *pylong}
  Return a C \ctype{long long} from a Python long integer.  If
  \var{pylong} cannot be represented as a \ctype{long long}, an
  \exception{OverflowError} will be raised.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{unsigned long long}{PyLong_AsUnsignedLongLong}{PyObject
                                                                 *pylong}
  Return a C \ctype{unsigned long long} from a Python long integer.
  If \var{pylong} cannot be represented as an \ctype{unsigned long
  long}, an \exception{OverflowError} will be raised if the value is
  positive, or a \exception{TypeError} will be raised if the value is
  negative.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{double}{PyLong_AsDouble}{PyObject *pylong}
  Returns a C \ctype{double} representation of the contents of
  \var{pylong}.  If \var{pylong} cannot be approximately represented
  as a \ctype{double}, an \exception{OverflowError} exception is
  raised and \code{-1.0} will be returned.
\end{cfuncdesc}

\begin{cfuncdesc}{void*}{PyLong_AsVoidPtr}{PyObject *pylong}
  Convert a Python integer or long integer \var{pylong} to a C
  \ctype{void} pointer.  If \var{pylong} cannot be converted, an
  \exception{OverflowError} will be raised.  This is only assured to
  produce a usable \ctype{void} pointer for values created with
  \cfunction{PyLong_FromVoidPtr()}.
  \versionadded{1.5.2}
\end{cfuncdesc}


\subsection{Floating Point Objects \label{floatObjects}}

\obindex{floating point}
\begin{ctypedesc}{PyFloatObject}
  This subtype of \ctype{PyObject} represents a Python floating point
  object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyFloat_Type}
  This instance of \ctype{PyTypeObject} represents the Python floating
  point type.  This is the same object as \code{types.FloatType}.
  \withsubitem{(in modules types)}{\ttindex{FloatType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyFloat_Check}{PyObject *p}
  Returns true if its argument is a \ctype{PyFloatObject} or a subtype
  of \ctype{PyFloatObject}.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyFloat_CheckExact}{PyObject *p}
  Returns true if its argument is a \ctype{PyFloatObject}, but not a
  subtype of \ctype{PyFloatObject}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyFloat_FromDouble}{double v}
  Creates a \ctype{PyFloatObject} object from \var{v}, or \NULL{} on
  failure.
\end{cfuncdesc}

\begin{cfuncdesc}{double}{PyFloat_AsDouble}{PyObject *pyfloat}
  Returns a C \ctype{double} representation of the contents of
  \var{pyfloat}.
\end{cfuncdesc}

\begin{cfuncdesc}{double}{PyFloat_AS_DOUBLE}{PyObject *pyfloat}
  Returns a C \ctype{double} representation of the contents of
  \var{pyfloat}, but without error checking.
\end{cfuncdesc}


\subsection{Complex Number Objects \label{complexObjects}}

\obindex{complex number}
Python's complex number objects are implemented as two distinct types
when viewed from the C API:  one is the Python object exposed to
Python programs, and the other is a C structure which represents the
actual complex number value.  The API provides functions for working
with both.

\subsubsection{Complex Numbers as C Structures}

Note that the functions which accept these structures as parameters
and return them as results do so \emph{by value} rather than
dereferencing them through pointers.  This is consistent throughout
the API.

\begin{ctypedesc}{Py_complex}
  The C structure which corresponds to the value portion of a Python
  complex number object.  Most of the functions for dealing with
  complex number objects use structures of this type as input or
  output values, as appropriate.  It is defined as:

\begin{verbatim}
typedef struct {
   double real;
   double imag;
} Py_complex;
\end{verbatim}
\end{ctypedesc}

\begin{cfuncdesc}{Py_complex}{_Py_c_sum}{Py_complex left, Py_complex right}
  Return the sum of two complex numbers, using the C
  \ctype{Py_complex} representation.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_complex}{_Py_c_diff}{Py_complex left, Py_complex right}
  Return the difference between two complex numbers, using the C
  \ctype{Py_complex} representation.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_complex}{_Py_c_neg}{Py_complex complex}
  Return the negation of the complex number \var{complex}, using the C
  \ctype{Py_complex} representation.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_complex}{_Py_c_prod}{Py_complex left, Py_complex right}
  Return the product of two complex numbers, using the C
  \ctype{Py_complex} representation.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_complex}{_Py_c_quot}{Py_complex dividend,
                                          Py_complex divisor}
  Return the quotient of two complex numbers, using the C
  \ctype{Py_complex} representation.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_complex}{_Py_c_pow}{Py_complex num, Py_complex exp}
  Return the exponentiation of \var{num} by \var{exp}, using the C
  \ctype{Py_complex} representation.
\end{cfuncdesc}


\subsubsection{Complex Numbers as Python Objects}

\begin{ctypedesc}{PyComplexObject}
  This subtype of \ctype{PyObject} represents a Python complex number
  object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyComplex_Type}
  This instance of \ctype{PyTypeObject} represents the Python complex
  number type.
\end{cvardesc}

\begin{cfuncdesc}{int}{PyComplex_Check}{PyObject *p}
  Returns true if its argument is a \ctype{PyComplexObject} or a
  subtype of \ctype{PyComplexObject}.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyComplex_CheckExact}{PyObject *p}
  Returns true if its argument is a \ctype{PyComplexObject}, but not a
  subtype of \ctype{PyComplexObject}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyComplex_FromCComplex}{Py_complex v}
  Create a new Python complex number object from a C
  \ctype{Py_complex} value.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyComplex_FromDoubles}{double real, double imag}
  Returns a new \ctype{PyComplexObject} object from \var{real} and
  \var{imag}.
\end{cfuncdesc}

\begin{cfuncdesc}{double}{PyComplex_RealAsDouble}{PyObject *op}
  Returns the real part of \var{op} as a C \ctype{double}.
\end{cfuncdesc}

\begin{cfuncdesc}{double}{PyComplex_ImagAsDouble}{PyObject *op}
  Returns the imaginary part of \var{op} as a C \ctype{double}.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_complex}{PyComplex_AsCComplex}{PyObject *op}
  Returns the \ctype{Py_complex} value of the complex number
  \var{op}.
\end{cfuncdesc}



\section{Sequence Objects \label{sequenceObjects}}

\obindex{sequence}
Generic operations on sequence objects were discussed in the previous
chapter; this section deals with the specific kinds of sequence
objects that are intrinsic to the Python language.


\subsection{String Objects \label{stringObjects}}

These functions raise \exception{TypeError} when expecting a string
parameter and are called with a non-string parameter.

\obindex{string}
\begin{ctypedesc}{PyStringObject}
  This subtype of \ctype{PyObject} represents a Python string object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyString_Type}
  This instance of \ctype{PyTypeObject} represents the Python string
  type; it is the same object as \code{types.TypeType} in the Python
  layer.
  \withsubitem{(in module types)}{\ttindex{StringType}}.
\end{cvardesc}

\begin{cfuncdesc}{int}{PyString_Check}{PyObject *o}
  Returns true if the object \var{o} is a string object or an instance
  of a subtype of the string type.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyString_CheckExact}{PyObject *o}
  Returns true if the object \var{o} is a string object, but not an
  instance of a subtype of the string type.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_FromString}{const char *v}
  Returns a new string object with the value \var{v} on success, and
  \NULL{} on failure.  The parameter \var{v} must not be \NULL; it
  will not be checked.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_FromStringAndSize}{const char *v,
                                                         int len}
  Returns a new string object with the value \var{v} and length
  \var{len} on success, and \NULL{} on failure.  If \var{v} is
  \NULL, the contents of the string are uninitialized.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_FromFormat}{const char *format, ...}
  Takes a C \cfunction{printf()}-style \var{format} string and a
  variable number of arguments, calculates the size of the resulting
  Python string and returns a string with the values formatted into
  it.  The variable arguments must be C types and must correspond
  exactly to the format characters in the \var{format} string.  The
  following format characters are allowed:

  \begin{tableiii}{l|l|l}{member}{Format Characters}{Type}{Comment}
    \lineiii{\%\%}{\emph{n/a}}{The literal \% character.}
    \lineiii{\%c}{int}{A single character, represented as an C int.}
    \lineiii{\%d}{int}{Exactly equivalent to \code{printf("\%d")}.}
    \lineiii{\%ld}{long}{Exactly equivalent to \code{printf("\%ld")}.}
    \lineiii{\%i}{int}{Exactly equivalent to \code{printf("\%i")}.}
    \lineiii{\%x}{int}{Exactly equivalent to \code{printf("\%x")}.}
    \lineiii{\%s}{char*}{A null-terminated C character array.}
    \lineiii{\%p}{void*}{The hex representation of a C pointer.
	Mostly equivalent to \code{printf("\%p")} except that it is
	guaranteed to start with the literal \code{0x} regardless of
	what the platform's \code{printf} yields.}
  \end{tableiii}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_FromFormatV}{const char *format,
                                                   va_list vargs}
  Identical to \function{PyString_FromFormat()} except that it takes
  exactly two arguments.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyString_Size}{PyObject *string}
  Returns the length of the string in string object \var{string}.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyString_GET_SIZE}{PyObject *string}
  Macro form of \cfunction{PyString_Size()} but without error
  checking.
\end{cfuncdesc}

\begin{cfuncdesc}{char*}{PyString_AsString}{PyObject *string}
  Returns a NUL-terminated representation of the contents of
  \var{string}.  The pointer refers to the internal buffer of
  \var{string}, not a copy.  The data must not be modified in any way,
  unless the string was just created using
  \code{PyString_FromStringAndSize(NULL, \var{size})}.
  It must not be deallocated.  If \var{string} is a Unicode object,
  this function computes the default encoding of \var{string} and
  operates on that.  If \var{string} is not a string object at all,
  \cfunction{PyString_AsString()} returns \NULL{} and raises
  \exception{TypeError}.
\end{cfuncdesc}

\begin{cfuncdesc}{char*}{PyString_AS_STRING}{PyObject *string}
  Macro form of \cfunction{PyString_AsString()} but without error
  checking.  Only string objects are supported; no Unicode objects
  should be passed.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyString_AsStringAndSize}{PyObject *obj,
                                                 char **buffer,
                                                 int *length}
  Returns a NUL-terminated representation of the contents of the
  object \var{obj} through the output variables \var{buffer} and
  \var{length}.

  The function accepts both string and Unicode objects as input. For
  Unicode objects it returns the default encoded version of the
  object.  If \var{length} is \NULL, the resulting buffer may not
  contain NUL characters; if it does, the function returns \code{-1}
  and a \exception{TypeError} is raised.

  The buffer refers to an internal string buffer of \var{obj}, not a
  copy. The data must not be modified in any way, unless the string
  was just created using \code{PyString_FromStringAndSize(NULL,
  \var{size})}.  It must not be deallocated.  If \var{string} is a
  Unicode object, this function computes the default encoding of
  \var{string} and operates on that.  If \var{string} is not a string
  object at all, \cfunction{PyString_AsString()} returns \NULL{} and
  raises \exception{TypeError}.
\end{cfuncdesc}

\begin{cfuncdesc}{void}{PyString_Concat}{PyObject **string,
                                         PyObject *newpart}
  Creates a new string object in \var{*string} containing the contents
  of \var{newpart} appended to \var{string}; the caller will own the
  new reference.  The reference to the old value of \var{string} will
  be stolen.  If the new string cannot be created, the old reference
  to \var{string} will still be discarded and the value of
  \var{*string} will be set to \NULL; the appropriate exception will
  be set.
\end{cfuncdesc}

\begin{cfuncdesc}{void}{PyString_ConcatAndDel}{PyObject **string,
                                               PyObject *newpart}
  Creates a new string object in \var{*string} containing the contents
  of \var{newpart} appended to \var{string}.  This version decrements
  the reference count of \var{newpart}.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{_PyString_Resize}{PyObject **string, int newsize}
  A way to resize a string object even though it is ``immutable''.
  Only use this to build up a brand new string object; don't use this
  if the string may already be known in other parts of the code.  It
  is an error to call this function if the refcount on the input string
  object is not one.
  Pass the address of an existing string object as an lvalue (it may
  be written into), and the new size desired.  On success, \var{*string}
  holds the resized string object and \code{0} is returned; the address in
  \var{*string} may differ from its input value.  If the
  reallocation fails, the original string object at \var{*string} is
  deallocated, \var{*string} is set to \NULL{}, a memory exception is set,
  and \code{-1} is returned.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_Format}{PyObject *format,
                                              PyObject *args}
  Returns a new string object from \var{format} and \var{args}.
  Analogous to \code{\var{format} \%\ \var{args}}.  The \var{args}
  argument must be a tuple.
\end{cfuncdesc}

\begin{cfuncdesc}{void}{PyString_InternInPlace}{PyObject **string}
  Intern the argument \var{*string} in place.  The argument must be
  the address of a pointer variable pointing to a Python string
  object.  If there is an existing interned string that is the same as
  \var{*string}, it sets \var{*string} to it (decrementing the
  reference count of the old string object and incrementing the
  reference count of the interned string object), otherwise it leaves
  \var{*string} alone and interns it (incrementing its reference
  count).  (Clarification: even though there is a lot of talk about
  reference counts, think of this function as reference-count-neutral;
  you own the object after the call if and only if you owned it before
  the call.)
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_InternFromString}{const char *v}
  A combination of \cfunction{PyString_FromString()} and
  \cfunction{PyString_InternInPlace()}, returning either a new string
  object that has been interned, or a new (``owned'') reference to an
  earlier interned string object with the same value.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_Decode}{const char *s,
                                               int size,
                                               const char *encoding,
                                               const char *errors}
  Creates an object by decoding \var{size} bytes of the encoded
  buffer \var{s} using the codec registered for
  \var{encoding}.  \var{encoding} and \var{errors} have the same
  meaning as the parameters of the same name in the
  \function{unicode()} built-in function.  The codec to be used is
  looked up using the Python codec registry.  Returns \NULL{} if
  an exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_AsDecodedObject}{PyObject *str,
                                               const char *encoding,
                                               const char *errors}
  Decodes a string object by passing it to the codec registered for
  \var{encoding} and returns the result as Python
  object. \var{encoding} and \var{errors} have the same meaning as the
  parameters of the same name in the string \method{encode()} method.
  The codec to be used is looked up using the Python codec registry.
  Returns \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_Encode}{const char *s,
                                               int size,
                                               const char *encoding,
                                               const char *errors}
  Encodes the \ctype{char} buffer of the given size by passing it to
  the codec registered for \var{encoding} and returns a Python object.
  \var{encoding} and \var{errors} have the same meaning as the
  parameters of the same name in the string \method{encode()} method.
  The codec to be used is looked up using the Python codec
  registry.  Returns \NULL{} if an exception was raised by the
  codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyString_AsEncodedObject}{PyObject *str,
                                               const char *encoding,
                                               const char *errors}
  Encodes a string object using the codec registered for
  \var{encoding} and returns the result as Python object.
  \var{encoding} and \var{errors} have the same meaning as the
  parameters of the same name in the string \method{encode()} method.
  The codec to be used is looked up using the Python codec registry.
  Returns \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}


\subsection{Unicode Objects \label{unicodeObjects}}
\sectionauthor{Marc-Andre Lemburg}{mal@lemburg.com}

%--- Unicode Type -------------------------------------------------------

These are the basic Unicode object types used for the Unicode
implementation in Python:

\begin{ctypedesc}{Py_UNICODE}
  This type represents a 16-bit unsigned storage type which is used by
  Python internally as basis for holding Unicode ordinals.  On
  platforms where \ctype{wchar_t} is available and also has 16-bits,
  \ctype{Py_UNICODE} is a typedef alias for \ctype{wchar_t} to enhance
  native platform compatibility.  On all other platforms,
  \ctype{Py_UNICODE} is a typedef alias for \ctype{unsigned short}.
\end{ctypedesc}

\begin{ctypedesc}{PyUnicodeObject}
  This subtype of \ctype{PyObject} represents a Python Unicode object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyUnicode_Type}
  This instance of \ctype{PyTypeObject} represents the Python Unicode
  type.
\end{cvardesc}

The following APIs are really C macros and can be used to do fast
checks and to access internal read-only data of Unicode objects:

\begin{cfuncdesc}{int}{PyUnicode_Check}{PyObject *o}
  Returns true if the object \var{o} is a Unicode object or an
  instance of a Unicode subtype.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_CheckExact}{PyObject *o}
  Returns true if the object \var{o} is a Unicode object, but not an
  instance of a subtype.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_GET_SIZE}{PyObject *o}
  Returns the size of the object.  \var{o} has to be a
  \ctype{PyUnicodeObject} (not checked).
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_GET_DATA_SIZE}{PyObject *o}
  Returns the size of the object's internal buffer in bytes.  \var{o}
  has to be a \ctype{PyUnicodeObject} (not checked).
\end{cfuncdesc}

\begin{cfuncdesc}{Py_UNICODE*}{PyUnicode_AS_UNICODE}{PyObject *o}
  Returns a pointer to the internal \ctype{Py_UNICODE} buffer of the
  object.  \var{o} has to be a \ctype{PyUnicodeObject} (not checked).
\end{cfuncdesc}

\begin{cfuncdesc}{const char*}{PyUnicode_AS_DATA}{PyObject *o}
  Returns a pointer to the internal buffer of the object.
  \var{o} has to be a \ctype{PyUnicodeObject} (not checked).
\end{cfuncdesc}

% --- Unicode character properties ---------------------------------------

Unicode provides many different character properties. The most often
needed ones are available through these macros which are mapped to C
functions depending on the Python configuration.

\begin{cfuncdesc}{int}{Py_UNICODE_ISSPACE}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is a whitespace
  character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISLOWER}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is a lowercase character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISUPPER}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is an uppercase
  character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISTITLE}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is a titlecase character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISLINEBREAK}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is a linebreak character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISDECIMAL}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is a decimal character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISDIGIT}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is a digit character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISNUMERIC}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is a numeric character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISALPHA}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is an alphabetic
  character.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_ISALNUM}{Py_UNICODE ch}
  Returns 1/0 depending on whether \var{ch} is an alphanumeric
  character.
\end{cfuncdesc}

These APIs can be used for fast direct character conversions:

\begin{cfuncdesc}{Py_UNICODE}{Py_UNICODE_TOLOWER}{Py_UNICODE ch}
  Returns the character \var{ch} converted to lower case.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_UNICODE}{Py_UNICODE_TOUPPER}{Py_UNICODE ch}
  Returns the character \var{ch} converted to upper case.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_UNICODE}{Py_UNICODE_TOTITLE}{Py_UNICODE ch}
  Returns the character \var{ch} converted to title case.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_TODECIMAL}{Py_UNICODE ch}
  Returns the character \var{ch} converted to a decimal positive
  integer.  Returns \code{-1} if this is not possible.  Does not raise
  exceptions.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{Py_UNICODE_TODIGIT}{Py_UNICODE ch}
  Returns the character \var{ch} converted to a single digit integer.
  Returns \code{-1} if this is not possible.  Does not raise
  exceptions.
\end{cfuncdesc}

\begin{cfuncdesc}{double}{Py_UNICODE_TONUMERIC}{Py_UNICODE ch}
  Returns the character \var{ch} converted to a (positive) double.
  Returns \code{-1.0} if this is not possible.  Does not raise
  exceptions.
\end{cfuncdesc}

% --- Plain Py_UNICODE ---------------------------------------------------

To create Unicode objects and access their basic sequence properties,
use these APIs:

\begin{cfuncdesc}{PyObject*}{PyUnicode_FromUnicode}{const Py_UNICODE *u,
                                                    int size}
  Create a Unicode Object from the Py_UNICODE buffer \var{u} of the
  given size. \var{u} may be \NULL{} which causes the contents to be
  undefined. It is the user's responsibility to fill in the needed
  data.  The buffer is copied into the new object. If the buffer is
  not \NULL, the return value might be a shared object. Therefore,
  modification of the resulting Unicode object is only allowed when
  \var{u} is \NULL.
\end{cfuncdesc}

\begin{cfuncdesc}{Py_UNICODE*}{PyUnicode_AsUnicode}{PyObject *unicode}
  Return a read-only pointer to the Unicode object's internal
  \ctype{Py_UNICODE} buffer, \NULL{} if \var{unicode} is not a Unicode
  object.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_GetSize}{PyObject *unicode}
  Return the length of the Unicode object.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_FromEncodedObject}{PyObject *obj,
                                                      const char *encoding,
                                                      const char *errors}
  Coerce an encoded object \var{obj} to an Unicode object and return a
  reference with incremented refcount.

  Coercion is done in the following way:

\begin{enumerate}
\item  Unicode objects are passed back as-is with incremented
       refcount. \note{These cannot be decoded; passing a non-\NULL{}
       value for encoding will result in a \exception{TypeError}.}

\item String and other char buffer compatible objects are decoded
      according to the given encoding and using the error handling
      defined by errors.  Both can be \NULL{} to have the interface
      use the default values (see the next section for details).

\item All other objects cause an exception.
\end{enumerate}

  The API returns \NULL{} if there was an error.  The caller is
  responsible for decref'ing the returned objects.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_FromObject}{PyObject *obj}
  Shortcut for \code{PyUnicode_FromEncodedObject(obj, NULL, "strict")}
  which is used throughout the interpreter whenever coercion to
  Unicode is needed.
\end{cfuncdesc}

% --- wchar_t support for platforms which support it ---------------------

If the platform supports \ctype{wchar_t} and provides a header file
wchar.h, Python can interface directly to this type using the
following functions. Support is optimized if Python's own
\ctype{Py_UNICODE} type is identical to the system's \ctype{wchar_t}.

\begin{cfuncdesc}{PyObject*}{PyUnicode_FromWideChar}{const wchar_t *w,
                                                     int size}
  Create a Unicode object from the \ctype{wchar_t} buffer \var{w} of
  the given size.  Returns \NULL{} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_AsWideChar}{PyUnicodeObject *unicode,
                                             wchar_t *w,
                                             int size}
  Copies the Unicode object contents into the \ctype{wchar_t} buffer
  \var{w}.  At most \var{size} \ctype{wchar_t} characters are copied.
  Returns the number of \ctype{wchar_t} characters copied or -1 in
  case of an error.
\end{cfuncdesc}


\subsubsection{Built-in Codecs \label{builtinCodecs}}

Python provides a set of builtin codecs which are written in C
for speed. All of these codecs are directly usable via the
following functions.

Many of the following APIs take two arguments encoding and
errors. These parameters encoding and errors have the same semantics
as the ones of the builtin unicode() Unicode object constructor.

Setting encoding to \NULL{} causes the default encoding to be used
which is \ASCII.  The file system calls should use
\cdata{Py_FileSystemDefaultEncoding} as the encoding for file
names. This variable should be treated as read-only: On some systems,
it will be a pointer to a static string, on others, it will change at
run-time, e.g. when the application invokes setlocale.

Error handling is set by errors which may also be set to \NULL{}
meaning to use the default handling defined for the codec.  Default
error handling for all builtin codecs is ``strict''
(\exception{ValueError} is raised).

The codecs all use a similar interface.  Only deviation from the
following generic ones are documented for simplicity.

% --- Generic Codecs -----------------------------------------------------

These are the generic codec APIs:

\begin{cfuncdesc}{PyObject*}{PyUnicode_Decode}{const char *s,
                                               int size,
                                               const char *encoding,
                                               const char *errors}
  Create a Unicode object by decoding \var{size} bytes of the encoded
  string \var{s}.  \var{encoding} and \var{errors} have the same
  meaning as the parameters of the same name in the
  \function{unicode()} builtin function.  The codec to be used is
  looked up using the Python codec registry.  Returns \NULL{} if an
  exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_Encode}{const Py_UNICODE *s,
                                               int size,
                                               const char *encoding,
                                               const char *errors}
  Encodes the \ctype{Py_UNICODE} buffer of the given size and returns
  a Python string object.  \var{encoding} and \var{errors} have the
  same meaning as the parameters of the same name in the Unicode
  \method{encode()} method.  The codec to be used is looked up using
  the Python codec registry.  Returns \NULL{} if an exception was
  raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsEncodedString}{PyObject *unicode,
                                               const char *encoding,
                                               const char *errors}
  Encodes a Unicode object and returns the result as Python string
  object. \var{encoding} and \var{errors} have the same meaning as the
  parameters of the same name in the Unicode \method{encode()} method.
  The codec to be used is looked up using the Python codec registry.
  Returns \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

% --- UTF-8 Codecs -------------------------------------------------------

These are the UTF-8 codec APIs:

\begin{cfuncdesc}{PyObject*}{PyUnicode_DecodeUTF8}{const char *s,
                                               int size,
                                               const char *errors}
  Creates a Unicode object by decoding \var{size} bytes of the UTF-8
  encoded string \var{s}. Returns \NULL{} if an exception was raised
  by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_EncodeUTF8}{const Py_UNICODE *s,
                                               int size,
                                               const char *errors}
  Encodes the \ctype{Py_UNICODE} buffer of the given size using UTF-8
  and returns a Python string object.  Returns \NULL{} if an exception
  was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsUTF8String}{PyObject *unicode}
  Encodes a Unicode objects using UTF-8 and returns the result as
  Python string object.  Error handling is ``strict''.  Returns
  \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

% --- UTF-16 Codecs ------------------------------------------------------ */

These are the UTF-16 codec APIs:

\begin{cfuncdesc}{PyObject*}{PyUnicode_DecodeUTF16}{const char *s,
                                               int size,
                                               const char *errors,
                                               int *byteorder}
  Decodes \var{length} bytes from a UTF-16 encoded buffer string and
  returns the corresponding Unicode object.  \var{errors} (if
  non-\NULL) defines the error handling. It defaults to ``strict''.

  If \var{byteorder} is non-\NULL, the decoder starts decoding using
  the given byte order:

\begin{verbatim}
   *byteorder == -1: little endian
   *byteorder == 0:  native order
   *byteorder == 1:  big endian
\end{verbatim}

  and then switches according to all byte order marks (BOM) it finds
  in the input data.  BOMs are not copied into the resulting Unicode
  string.  After completion, \var{*byteorder} is set to the current
  byte order at the end of input data.

  If \var{byteorder} is \NULL, the codec starts in native order mode.

  Returns \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_EncodeUTF16}{const Py_UNICODE *s,
                                               int size,
                                               const char *errors,
                                               int byteorder}
  Returns a Python string object holding the UTF-16 encoded value of
  the Unicode data in \var{s}.  If \var{byteorder} is not \code{0},
  output is written according to the following byte order:

\begin{verbatim}
   byteorder == -1: little endian
   byteorder == 0:  native byte order (writes a BOM mark)
   byteorder == 1:  big endian
\end{verbatim}

  If byteorder is \code{0}, the output string will always start with
  the Unicode BOM mark (U+FEFF). In the other two modes, no BOM mark
  is prepended.

  Note that \ctype{Py_UNICODE} data is being interpreted as UTF-16
  reduced to UCS-2. This trick makes it possible to add full UTF-16
  capabilities at a later point without comprimising the APIs.

  Returns \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsUTF16String}{PyObject *unicode}
  Returns a Python string using the UTF-16 encoding in native byte
  order. The string always starts with a BOM mark.  Error handling is
  ``strict''.  Returns \NULL{} if an exception was raised by the
  codec.
\end{cfuncdesc}

% --- Unicode-Escape Codecs ----------------------------------------------

These are the ``Unicode Esacpe'' codec APIs:

\begin{cfuncdesc}{PyObject*}{PyUnicode_DecodeUnicodeEscape}{const char *s,
                                               int size,
                                               const char *errors}
  Creates a Unicode object by decoding \var{size} bytes of the
  Unicode-Escape encoded string \var{s}.  Returns \NULL{} if an
  exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_EncodeUnicodeEscape}{const Py_UNICODE *s,
                                               int size,
                                               const char *errors}
  Encodes the \ctype{Py_UNICODE} buffer of the given size using
  Unicode-Escape and returns a Python string object.  Returns \NULL{}
  if an exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsUnicodeEscapeString}{PyObject *unicode}
  Encodes a Unicode objects using Unicode-Escape and returns the
  result as Python string object.  Error handling is ``strict''.
  Returns \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

% --- Raw-Unicode-Escape Codecs ------------------------------------------

These are the ``Raw Unicode Esacpe'' codec APIs:

\begin{cfuncdesc}{PyObject*}{PyUnicode_DecodeRawUnicodeEscape}{const char *s,
                                               int size,
                                               const char *errors}
  Creates a Unicode object by decoding \var{size} bytes of the
  Raw-Unicode-Esacpe encoded string \var{s}.  Returns \NULL{} if an
  exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_EncodeRawUnicodeEscape}{const Py_UNICODE *s,
                                               int size,
                                               const char *errors}
  Encodes the \ctype{Py_UNICODE} buffer of the given size using
  Raw-Unicode-Escape and returns a Python string object.  Returns
  \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsRawUnicodeEscapeString}{PyObject *unicode}
  Encodes a Unicode objects using Raw-Unicode-Escape and returns the
  result as Python string object. Error handling is ``strict''.
  Returns \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

% --- Latin-1 Codecs -----------------------------------------------------

These are the Latin-1 codec APIs:
Latin-1 corresponds to the first 256 Unicode ordinals and only these
are accepted by the codecs during encoding.

\begin{cfuncdesc}{PyObject*}{PyUnicode_DecodeLatin1}{const char *s,
                                                     int size,
                                                     const char *errors}
  Creates a Unicode object by decoding \var{size} bytes of the Latin-1
  encoded string \var{s}.  Returns \NULL{} if an exception was raised
  by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_EncodeLatin1}{const Py_UNICODE *s,
                                                     int size,
                                                     const char *errors}
  Encodes the \ctype{Py_UNICODE} buffer of the given size using
  Latin-1 and returns a Python string object.  Returns \NULL{} if an
  exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsLatin1String}{PyObject *unicode}
  Encodes a Unicode objects using Latin-1 and returns the result as
  Python string object.  Error handling is ``strict''.  Returns
  \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

% --- ASCII Codecs -------------------------------------------------------

These are the \ASCII{} codec APIs.  Only 7-bit \ASCII{} data is
accepted. All other codes generate errors.

\begin{cfuncdesc}{PyObject*}{PyUnicode_DecodeASCII}{const char *s,
                                                    int size,
                                                    const char *errors}
  Creates a Unicode object by decoding \var{size} bytes of the
  \ASCII{} encoded string \var{s}.  Returns \NULL{} if an exception
  was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_EncodeASCII}{const Py_UNICODE *s,
                                                    int size,
                                                    const char *errors}
  Encodes the \ctype{Py_UNICODE} buffer of the given size using
  \ASCII{} and returns a Python string object.  Returns \NULL{} if an
  exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsASCIIString}{PyObject *unicode}
  Encodes a Unicode objects using \ASCII{} and returns the result as
  Python string object.  Error handling is ``strict''.  Returns
  \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

% --- Character Map Codecs -----------------------------------------------

These are the mapping codec APIs:

This codec is special in that it can be used to implement many
different codecs (and this is in fact what was done to obtain most of
the standard codecs included in the \module{encodings} package). The
codec uses mapping to encode and decode characters.

Decoding mappings must map single string characters to single Unicode
characters, integers (which are then interpreted as Unicode ordinals)
or None (meaning "undefined mapping" and causing an error).

Encoding mappings must map single Unicode characters to single string
characters, integers (which are then interpreted as Latin-1 ordinals)
or None (meaning "undefined mapping" and causing an error).

The mapping objects provided must only support the __getitem__ mapping
interface.

If a character lookup fails with a LookupError, the character is
copied as-is meaning that its ordinal value will be interpreted as
Unicode or Latin-1 ordinal resp. Because of this, mappings only need
to contain those mappings which map characters to different code
points.

\begin{cfuncdesc}{PyObject*}{PyUnicode_DecodeCharmap}{const char *s,
                                               int size,
                                               PyObject *mapping,
                                               const char *errors}
  Creates a Unicode object by decoding \var{size} bytes of the encoded
  string \var{s} using the given \var{mapping} object.  Returns
  \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_EncodeCharmap}{const Py_UNICODE *s,
                                               int size,
                                               PyObject *mapping,
                                               const char *errors}
  Encodes the \ctype{Py_UNICODE} buffer of the given size using the
  given \var{mapping} object and returns a Python string object.
  Returns \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsCharmapString}{PyObject *unicode,
                                                        PyObject *mapping}
  Encodes a Unicode objects using the given \var{mapping} object and
  returns the result as Python string object.  Error handling is
  ``strict''.  Returns \NULL{} if an exception was raised by the
  codec.
\end{cfuncdesc}

The following codec API is special in that maps Unicode to Unicode.

\begin{cfuncdesc}{PyObject*}{PyUnicode_TranslateCharmap}{const Py_UNICODE *s,
                                               int size,
                                               PyObject *table,
                                               const char *errors}
  Translates a \ctype{Py_UNICODE} buffer of the given length by
  applying a character mapping \var{table} to it and returns the
  resulting Unicode object.  Returns \NULL{} when an exception was
  raised by the codec.

  The \var{mapping} table must map Unicode ordinal integers to Unicode
  ordinal integers or None (causing deletion of the character).

  Mapping tables need only provide the method{__getitem__()}
  interface; dictionaries and sequences work well.  Unmapped character
  ordinals (ones which cause a \exception{LookupError}) are left
  untouched and are copied as-is.
\end{cfuncdesc}

% --- MBCS codecs for Windows --------------------------------------------

These are the MBCS codec APIs. They are currently only available on
Windows and use the Win32 MBCS converters to implement the
conversions.  Note that MBCS (or DBCS) is a class of encodings, not
just one.  The target encoding is defined by the user settings on the
machine running the codec.

\begin{cfuncdesc}{PyObject*}{PyUnicode_DecodeMBCS}{const char *s,
                                               int size,
                                               const char *errors}
  Creates a Unicode object by decoding \var{size} bytes of the MBCS
  encoded string \var{s}.  Returns \NULL{} if an exception was
  raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_EncodeMBCS}{const Py_UNICODE *s,
                                               int size,
                                               const char *errors}
  Encodes the \ctype{Py_UNICODE} buffer of the given size using MBCS
  and returns a Python string object.  Returns \NULL{} if an exception
  was raised by the codec.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_AsMBCSString}{PyObject *unicode}
  Encodes a Unicode objects using MBCS and returns the result as
  Python string object.  Error handling is ``strict''.  Returns
  \NULL{} if an exception was raised by the codec.
\end{cfuncdesc}

% --- Methods & Slots ----------------------------------------------------

\subsubsection{Methods and Slot Functions \label{unicodeMethodsAndSlots}}

The following APIs are capable of handling Unicode objects and strings
on input (we refer to them as strings in the descriptions) and return
Unicode objects or integers as apporpriate.

They all return \NULL{} or \code{-1} if an exception occurs.

\begin{cfuncdesc}{PyObject*}{PyUnicode_Concat}{PyObject *left,
                                               PyObject *right}
  Concat two strings giving a new Unicode string.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_Split}{PyObject *s,
                                              PyObject *sep,
                                              int maxsplit}
  Split a string giving a list of Unicode strings.  If sep is \NULL,
  splitting will be done at all whitespace substrings.  Otherwise,
  splits occur at the given separator.  At most \var{maxsplit} splits
  will be done.  If negative, no limit is set.  Separators are not
  included in the resulting list.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_Splitlines}{PyObject *s,
                                                   int maxsplit}
  Split a Unicode string at line breaks, returning a list of Unicode
  strings.  CRLF is considered to be one line break.  The Line break
  characters are not included in the resulting strings.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_Translate}{PyObject *str,
                                                  PyObject *table,
                                                  const char *errors}
  Translate a string by applying a character mapping table to it and
  return the resulting Unicode object.

  The mapping table must map Unicode ordinal integers to Unicode
  ordinal integers or None (causing deletion of the character).

  Mapping tables need only provide the \method{__getitem__()}
  interface; dictionaries and sequences work well.  Unmapped character
  ordinals (ones which cause a \exception{LookupError}) are left
  untouched and are copied as-is.

  \var{errors} has the usual meaning for codecs. It may be \NULL{}
  which indicates to use the default error handling.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_Join}{PyObject *separator,
                                             PyObject *seq}
  Join a sequence of strings using the given separator and return the
  resulting Unicode string.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_Tailmatch}{PyObject *str,
                                                  PyObject *substr,
                                                  int start,
                                                  int end,
                                                  int direction}
  Return 1 if \var{substr} matches \var{str}[\var{start}:\var{end}] at
  the given tail end (\var{direction} == -1 means to do a prefix
  match, \var{direction} == 1 a suffix match), 0 otherwise.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_Find}{PyObject *str,
                                       PyObject *substr,
                                       int start,
                                       int end,
                                       int direction}
  Return the first position of \var{substr} in
  \var{str}[\var{start}:\var{end}] using the given \var{direction}
  (\var{direction} == 1 means to do a forward search,
  \var{direction} == -1 a backward search).  The return value is the
  index of the first match; a value of \code{-1} indicates that no
  match was found, and \code{-2} indicates that an error occurred and
  an exception has been set.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_Count}{PyObject *str,
                                        PyObject *substr,
                                        int start,
                                        int end}
  Return the number of non-overlapping occurrences of \var{substr} in
  \code{\var{str}[\var{start}:\var{end}]}.  Returns \code{-1} if an
  error occurred.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_Replace}{PyObject *str,
                                                PyObject *substr,
                                                PyObject *replstr,
                                                int maxcount}
  Replace at most \var{maxcount} occurrences of \var{substr} in
  \var{str} with \var{replstr} and return the resulting Unicode object.
  \var{maxcount} == -1 means replace all occurrences.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_Compare}{PyObject *left, PyObject *right}
  Compare two strings and return -1, 0, 1 for less than, equal, and
  greater than, respectively.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyUnicode_Format}{PyObject *format,
                                              PyObject *args}
  Returns a new string object from \var{format} and \var{args}; this
  is analogous to \code{\var{format} \%\ \var{args}}.  The
  \var{args} argument must be a tuple.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyUnicode_Contains}{PyObject *container,
                                           PyObject *element}
  Checks whether \var{element} is contained in \var{container} and
  returns true or false accordingly.

  \var{element} has to coerce to a one element Unicode
  string. \code{-1} is returned if there was an error.
\end{cfuncdesc}


\subsection{Buffer Objects \label{bufferObjects}}
\sectionauthor{Greg Stein}{gstein@lyra.org}

\obindex{buffer}
Python objects implemented in C can export a group of functions called
the ``buffer\index{buffer interface} interface.''  These functions can
be used by an object to expose its data in a raw, byte-oriented
format. Clients of the object can use the buffer interface to access
the object data directly, without needing to copy it first.

Two examples of objects that support
the buffer interface are strings and arrays. The string object exposes
the character contents in the buffer interface's byte-oriented
form. An array can also expose its contents, but it should be noted
that array elements may be multi-byte values.

An example user of the buffer interface is the file object's
\method{write()} method. Any object that can export a series of bytes
through the buffer interface can be written to a file. There are a
number of format codes to \cfunction{PyArg_ParseTuple()} that operate
against an object's buffer interface, returning data from the target
object.

More information on the buffer interface is provided in the section
``Buffer Object Structures'' (section~\ref{buffer-structs}), under
the description for \ctype{PyBufferProcs}\ttindex{PyBufferProcs}.

A ``buffer object'' is defined in the \file{bufferobject.h} header
(included by \file{Python.h}). These objects look very similar to
string objects at the Python programming level: they support slicing,
indexing, concatenation, and some other standard string
operations. However, their data can come from one of two sources: from
a block of memory, or from another object which exports the buffer
interface.

Buffer objects are useful as a way to expose the data from another
object's buffer interface to the Python programmer. They can also be
used as a zero-copy slicing mechanism. Using their ability to
reference a block of memory, it is possible to expose any data to the
Python programmer quite easily. The memory could be a large, constant
array in a C extension, it could be a raw block of memory for
manipulation before passing to an operating system library, or it
could be used to pass around structured data in its native, in-memory
format.

\begin{ctypedesc}{PyBufferObject}
  This subtype of \ctype{PyObject} represents a buffer object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyBuffer_Type}
  The instance of \ctype{PyTypeObject} which represents the Python
  buffer type; it is the same object as \code{types.BufferType} in the
  Python layer.\withsubitem{(in module types)}{\ttindex{BufferType}}.
\end{cvardesc}

\begin{cvardesc}{int}{Py_END_OF_BUFFER}
  This constant may be passed as the \var{size} parameter to
  \cfunction{PyBuffer_FromObject()} or
  \cfunction{PyBuffer_FromReadWriteObject()}.  It indicates that the
  new \ctype{PyBufferObject} should refer to \var{base} object from
  the specified \var{offset} to the end of its exported buffer.  Using
  this enables the caller to avoid querying the \var{base} object for
  its length.
\end{cvardesc}

\begin{cfuncdesc}{int}{PyBuffer_Check}{PyObject *p}
  Return true if the argument has type \cdata{PyBuffer_Type}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyBuffer_FromObject}{PyObject *base,
                                                  int offset, int size}
  Return a new read-only buffer object.  This raises
  \exception{TypeError} if \var{base} doesn't support the read-only
  buffer protocol or doesn't provide exactly one buffer segment, or it
  raises \exception{ValueError} if \var{offset} is less than zero. The
  buffer will hold a reference to the \var{base} object, and the
  buffer's contents will refer to the \var{base} object's buffer
  interface, starting as position \var{offset} and extending for
  \var{size} bytes. If \var{size} is \constant{Py_END_OF_BUFFER}, then
  the new buffer's contents extend to the length of the \var{base}
  object's exported buffer data.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyBuffer_FromReadWriteObject}{PyObject *base,
                                                           int offset,
                                                           int size}
  Return a new writable buffer object.  Parameters and exceptions are
  similar to those for \cfunction{PyBuffer_FromObject()}.  If the
  \var{base} object does not export the writeable buffer protocol,
  then \exception{TypeError} is raised.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyBuffer_FromMemory}{void *ptr, int size}
  Return a new read-only buffer object that reads from a specified
  location in memory, with a specified size.  The caller is
  responsible for ensuring that the memory buffer, passed in as
  \var{ptr}, is not deallocated while the returned buffer object
  exists.  Raises \exception{ValueError} if \var{size} is less than
  zero.  Note that \constant{Py_END_OF_BUFFER} may \emph{not} be
  passed for the \var{size} parameter; \exception{ValueError} will be
  raised in that case.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyBuffer_FromReadWriteMemory}{void *ptr, int size}
  Similar to \cfunction{PyBuffer_FromMemory()}, but the returned
  buffer is writable.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyBuffer_New}{int size}
  Returns a new writable buffer object that maintains its own memory
  buffer of \var{size} bytes.  \exception{ValueError} is returned if
  \var{size} is not zero or positive.
\end{cfuncdesc}


\subsection{Tuple Objects \label{tupleObjects}}

\obindex{tuple}
\begin{ctypedesc}{PyTupleObject}
  This subtype of \ctype{PyObject} represents a Python tuple object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyTuple_Type}
  This instance of \ctype{PyTypeObject} represents the Python tuple
  type; it is the same object as \code{types.TupleType} in the Python
  layer.\withsubitem{(in module types)}{\ttindex{TupleType}}.
\end{cvardesc}

\begin{cfuncdesc}{int}{PyTuple_Check}{PyObject *p}
  Return true if \var{p} is a tuple object or an instance of a subtype
  of the tuple type.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyTuple_CheckExact}{PyObject *p}
  Return true if \var{p} is a tuple object, but not an instance of a
  subtype of the tuple type.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyTuple_New}{int len}
  Return a new tuple object of size \var{len}, or \NULL{} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyTuple_Size}{PyObject *p}
  Takes a pointer to a tuple object, and returns the size of that
  tuple.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyTuple_GET_SIZE}{PyObject *p}
  Return the size of the tuple \var{p}, which must be non-\NULL{} and
  point to a tuple; no error checking is performed.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyTuple_GetItem}{PyObject *p, int pos}
  Returns the object at position \var{pos} in the tuple pointed to by
  \var{p}.  If \var{pos} is out of bounds, returns \NULL{} and sets an
  \exception{IndexError} exception.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyTuple_GET_ITEM}{PyObject *p, int pos}
  Like \cfunction{PyTuple_GetItem()}, but does no checking of its
  arguments.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyTuple_GetSlice}{PyObject *p,
                                               int low, int high}
  Takes a slice of the tuple pointed to by \var{p} from \var{low} to
  \var{high} and returns it as a new tuple.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyTuple_SetItem}{PyObject *p,
                                        int pos, PyObject *o}
  Inserts a reference to object \var{o} at position \var{pos} of the
  tuple pointed to by \var{p}. It returns \code{0} on success.
  \note{This function ``steals'' a reference to \var{o}.}
\end{cfuncdesc}

\begin{cfuncdesc}{void}{PyTuple_SET_ITEM}{PyObject *p,
                                          int pos, PyObject *o}
  Like \cfunction{PyTuple_SetItem()}, but does no error checking, and
  should \emph{only} be used to fill in brand new tuples.  \note{This
  function ``steals'' a reference to \var{o}.}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{_PyTuple_Resize}{PyObject **p, int newsize}
  Can be used to resize a tuple.  \var{newsize} will be the new length
  of the tuple.  Because tuples are \emph{supposed} to be immutable,
  this should only be used if there is only one reference to the
  object.  Do \emph{not} use this if the tuple may already be known to
  some other part of the code.  The tuple will always grow or shrink
  at the end.  Think of this as destroying the old tuple and creating
  a new one, only more efficiently.  Returns \code{0} on success.
  Client code should never assume that the resulting value of
  \code{*\var{p}} will be the same as before calling this function.
  If the object referenced by \code{*\var{p}} is replaced, the
  original \code{*\var{p}} is destroyed.  On failure, returns
  \code{-1} and sets \code{*\var{p}} to \NULL, and raises
  \exception{MemoryError} or
  \exception{SystemError}.
  \versionchanged[Removed unused third parameter, \var{last_is_sticky}]{2.2}
\end{cfuncdesc}


\subsection{List Objects \label{listObjects}}

\obindex{list}
\begin{ctypedesc}{PyListObject}
  This subtype of \ctype{PyObject} represents a Python list object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyList_Type}
  This instance of \ctype{PyTypeObject} represents the Python list
  type.  This is the same object as \code{types.ListType}.
  \withsubitem{(in module types)}{\ttindex{ListType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyList_Check}{PyObject *p}
  Returns true if its argument is a \ctype{PyListObject}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyList_New}{int len}
  Returns a new list of length \var{len} on success, or \NULL{} on
  failure.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyList_Size}{PyObject *list}
  Returns the length of the list object in \var{list}; this is
  equivalent to \samp{len(\var{list})} on a list object.
  \bifuncindex{len}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyList_GET_SIZE}{PyObject *list}
  Macro form of \cfunction{PyList_Size()} without error checking.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyList_GetItem}{PyObject *list, int index}
  Returns the object at position \var{pos} in the list pointed to by
  \var{p}.  If \var{pos} is out of bounds, returns \NULL{} and sets an
  \exception{IndexError} exception.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyList_GET_ITEM}{PyObject *list, int i}
  Macro form of \cfunction{PyList_GetItem()} without error checking.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyList_SetItem}{PyObject *list, int index,
                                       PyObject *item}
  Sets the item at index \var{index} in list to \var{item}.  Returns
  \code{0} on success or \code{-1} on failure.  \note{This function
  ``steals'' a reference to \var{item} and discards a reference to an
  item already in the list at the affected position.}
\end{cfuncdesc}

\begin{cfuncdesc}{void}{PyList_SET_ITEM}{PyObject *list, int i,
                                              PyObject *o}
  Macro form of \cfunction{PyList_SetItem()} without error checking.
  This is normally only used to fill in new lists where there is no
  previous content.
  \note{This function ``steals'' a reference to \var{item}, and,
  unlike \cfunction{PyList_SetItem()}, does \emph{not} discard a
  reference to any item that it being replaced; any reference in
  \var{list} at position \var{i} will be leaked.}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyList_Insert}{PyObject *list, int index,
                                      PyObject *item}
  Inserts the item \var{item} into list \var{list} in front of index
  \var{index}.  Returns \code{0} if successful; returns \code{-1} and
  raises an exception if unsuccessful.  Analogous to
  \code{\var{list}.insert(\var{index}, \var{item})}.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyList_Append}{PyObject *list, PyObject *item}
  Appends the object \var{item} at the end of list \var{list}.
  Returns \code{0} if successful; returns \code{-1} and sets an
  exception if unsuccessful.  Analogous to
  \code{\var{list}.append(\var{item})}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyList_GetSlice}{PyObject *list,
                                              int low, int high}
  Returns a list of the objects in \var{list} containing the objects
  \emph{between} \var{low} and \var{high}.  Returns \NULL{} and sets
  an exception if unsuccessful.
  Analogous to \code{\var{list}[\var{low}:\var{high}]}.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyList_SetSlice}{PyObject *list,
                                        int low, int high,
                                        PyObject *itemlist}
  Sets the slice of \var{list} between \var{low} and \var{high} to the
  contents of \var{itemlist}.  Analogous to
  \code{\var{list}[\var{low}:\var{high}] = \var{itemlist}}.  Returns
  \code{0} on success, \code{-1} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyList_Sort}{PyObject *list}
  Sorts the items of \var{list} in place.  Returns \code{0} on
  success, \code{-1} on failure.  This is equivalent to
  \samp{\var{list}.sort()}.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyList_Reverse}{PyObject *list}
  Reverses the items of \var{list} in place.  Returns \code{0} on
  success, \code{-1} on failure.  This is the equivalent of
  \samp{\var{list}.reverse()}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyList_AsTuple}{PyObject *list}
  Returns a new tuple object containing the contents of \var{list};
  equivalent to \samp{tuple(\var{list})}.\bifuncindex{tuple}
\end{cfuncdesc}


\section{Mapping Objects \label{mapObjects}}

\obindex{mapping}


\subsection{Dictionary Objects \label{dictObjects}}

\obindex{dictionary}
\begin{ctypedesc}{PyDictObject}
  This subtype of \ctype{PyObject} represents a Python dictionary
  object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyDict_Type}
  This instance of \ctype{PyTypeObject} represents the Python
  dictionary type.  This is exposed to Python programs as
  \code{types.DictType} and \code{types.DictionaryType}.
  \withsubitem{(in module types)}{\ttindex{DictType}\ttindex{DictionaryType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyDict_Check}{PyObject *p}
  Returns true if its argument is a \ctype{PyDictObject}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDict_New}{}
  Returns a new empty dictionary, or \NULL{} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDictProxy_New}{PyObject *dict}
  Return a proxy object for a mapping which enforces read-only
  behavior.  This is normally used to create a proxy to prevent
  modification of the dictionary for non-dynamic class types.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{void}{PyDict_Clear}{PyObject *p}
  Empties an existing dictionary of all key-value pairs.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDict_Copy}{PyObject *p}
  Returns a new dictionary that contains the same key-value pairs as
  \var{p}.
  \versionadded{1.6}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_SetItem}{PyObject *p, PyObject *key,
                                       PyObject *val}
  Inserts \var{value} into the dictionary \var{p} with a key of
  \var{key}.  \var{key} must be hashable; if it isn't,
  \exception{TypeError} will be raised.
  Returns \code{0} on success or \code{-1} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_SetItemString}{PyObject *p,
            char *key,
            PyObject *val}
  Inserts \var{value} into the dictionary \var{p} using \var{key} as a
  key. \var{key} should be a \ctype{char*}.  The key object is created
  using \code{PyString_FromString(\var{key})}. Returns \code{0} on
  success or \code{-1} on failure.
  \ttindex{PyString_FromString()}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_DelItem}{PyObject *p, PyObject *key}
  Removes the entry in dictionary \var{p} with key \var{key}.
  \var{key} must be hashable; if it isn't, \exception{TypeError} is
  raised.  Returns \code{0} on success or \code{-1} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_DelItemString}{PyObject *p, char *key}
  Removes the entry in dictionary \var{p} which has a key specified by
  the string \var{key}.  Returns \code{0} on success or \code{-1} on
  failure.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDict_GetItem}{PyObject *p, PyObject *key}
  Returns the object from dictionary \var{p} which has a key
  \var{key}.  Returns \NULL{} if the key \var{key} is not present, but
  \emph{without} setting an exception.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDict_GetItemString}{PyObject *p, char *key}
  This is the same as \cfunction{PyDict_GetItem()}, but \var{key} is
  specified as a \ctype{char*}, rather than a \ctype{PyObject*}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDict_Items}{PyObject *p}
  Returns a \ctype{PyListObject} containing all the items from the
  dictionary, as in the dictinoary method \method{items()} (see the
  \citetitle[../lib/lib.html]{Python Library Reference}).
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDict_Keys}{PyObject *p}
  Returns a \ctype{PyListObject} containing all the keys from the
  dictionary, as in the dictionary method \method{keys()} (see the
  \citetitle[../lib/lib.html]{Python Library Reference}).
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDict_Values}{PyObject *p}
  Returns a \ctype{PyListObject} containing all the values from the
  dictionary \var{p}, as in the dictionary method \method{values()}
  (see the \citetitle[../lib/lib.html]{Python Library Reference}).
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_Size}{PyObject *p}
  Returns the number of items in the dictionary.  This is equivalent
  to \samp{len(\var{p})} on a dictionary.\bifuncindex{len}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_Next}{PyObject *p, int *ppos,
                                    PyObject **pkey, PyObject **pvalue}
  Iterate over all key-value pairs in the dictionary \var{p}.  The
  \ctype{int} referred to by \var{ppos} must be initialized to
  \code{0} prior to the first call to this function to start the
  iteration; the function returns true for each pair in the
  dictionary, and false once all pairs have been reported.  The
  parameters \var{pkey} and \var{pvalue} should either point to
  \ctype{PyObject*} variables that will be filled in with each key and
  value, respectively, or may be \NULL.  Any references returned through
  them are borrowed.

  For example:

\begin{verbatim}
PyObject *key, *value;
int pos = 0;

while (PyDict_Next(self->dict, &pos, &key, &value)) {
    /* do something interesting with the values... */
    ...
}
\end{verbatim}

  The dictionary \var{p} should not be mutated during iteration.  It
  is safe (since Python 2.1) to modify the values of the keys as you
  iterate over the dictionary, but only so long as the set of keys
  does not change.  For example:

\begin{verbatim}
PyObject *key, *value;
int pos = 0;

while (PyDict_Next(self->dict, &pos, &key, &value)) {
    int i = PyInt_AS_LONG(value) + 1;
    PyObject *o = PyInt_FromLong(i);
    if (o == NULL)
        return -1;
    if (PyDict_SetItem(self->dict, key, o) < 0) {
        Py_DECREF(o);
        return -1;
    }
    Py_DECREF(o);
}
\end{verbatim}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_Merge}{PyObject *a, PyObject *b, int override}
  Iterate over mapping object \var{b} adding key-value pairs to dictionary
  \var{a}.
  \var{b} may be a dictionary, or any object supporting
  \function{PyMapping_Keys()} and \function{PyObject_GetItem()}.
  If \var{override} is true, existing pairs in \var{a} will
  be replaced if a matching key is found in \var{b}, otherwise pairs
  will only be added if there is not a matching key in \var{a}.
  Return \code{0} on success or \code{-1} if an exception was
  raised.
\versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_Update}{PyObject *a, PyObject *b}
  This is the same as \code{PyDict_Merge(\var{a}, \var{b}, 1)} in C,
  or \code{\var{a}.update(\var{b})} in Python.  Return \code{0} on
  success or \code{-1} if an exception was raised.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDict_MergeFromSeq2}{PyObject *a, PyObject *seq2,
                                             int override}
  Update or merge into dictionary \var{a}, from the key-value pairs in
  \var{seq2}.  \var{seq2} must be an iterable object producing
  iterable objects of length 2, viewed as key-value pairs.  In case of
  duplicate keys, the last wins if \var{override} is true, else the
  first wins.
  Return \code{0} on success or \code{-1} if an exception
  was raised.
  Equivalent Python (except for the return value):

\begin{verbatim}
def PyDict_MergeFromSeq2(a, seq2, override):
    for key, value in seq2:
        if override or key not in a:
            a[key] = value
\end{verbatim}

  \versionadded{2.2}
\end{cfuncdesc}


\section{Other Objects \label{otherObjects}}

\subsection{File Objects \label{fileObjects}}

\obindex{file}
Python's built-in file objects are implemented entirely on the
\ctype{FILE*} support from the C standard library.  This is an
implementation detail and may change in future releases of Python.

\begin{ctypedesc}{PyFileObject}
  This subtype of \ctype{PyObject} represents a Python file object.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyFile_Type}
  This instance of \ctype{PyTypeObject} represents the Python file
  type.  This is exposed to Python programs as \code{types.FileType}.
  \withsubitem{(in module types)}{\ttindex{FileType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyFile_Check}{PyObject *p}
  Returns true if its argument is a \ctype{PyFileObject} or a subtype
  of \ctype{PyFileObject}.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyFile_CheckExact}{PyObject *p}
  Returns true if its argument is a \ctype{PyFileObject}, but not a
  subtype of \ctype{PyFileObject}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyFile_FromString}{char *filename, char *mode}
  On success, returns a new file object that is opened on the file
  given by \var{filename}, with a file mode given by \var{mode}, where
  \var{mode} has the same semantics as the standard C routine
  \cfunction{fopen()}\ttindex{fopen()}.  On failure, returns \NULL.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyFile_FromFile}{FILE *fp,
                                              char *name, char *mode,
                                              int (*close)(FILE*)}
  Creates a new \ctype{PyFileObject} from the already-open standard C
  file pointer, \var{fp}.  The function \var{close} will be called
  when the file should be closed.  Returns \NULL{} on failure.
\end{cfuncdesc}

\begin{cfuncdesc}{FILE*}{PyFile_AsFile}{PyFileObject *p}
  Returns the file object associated with \var{p} as a \ctype{FILE*}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyFile_GetLine}{PyObject *p, int n}
  Equivalent to \code{\var{p}.readline(\optional{\var{n}})}, this
  function reads one line from the object \var{p}.  \var{p} may be a
  file object or any object with a \method{readline()} method.  If
  \var{n} is \code{0}, exactly one line is read, regardless of the
  length of the line.  If \var{n} is greater than \code{0}, no more
  than \var{n} bytes will be read from the file; a partial line can be
  returned.  In both cases, an empty string is returned if the end of
  the file is reached immediately.  If \var{n} is less than \code{0},
  however, one line is read regardless of length, but
  \exception{EOFError} is raised if the end of the file is reached
  immediately.
  \withsubitem{(built-in exception)}{\ttindex{EOFError}}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyFile_Name}{PyObject *p}
  Returns the name of the file specified by \var{p} as a string
  object.
\end{cfuncdesc}

\begin{cfuncdesc}{void}{PyFile_SetBufSize}{PyFileObject *p, int n}
  Available on systems with \cfunction{setvbuf()}\ttindex{setvbuf()}
  only.  This should only be called immediately after file object
  creation.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyFile_SoftSpace}{PyObject *p, int newflag}
  This function exists for internal use by the interpreter.  Sets the
  \member{softspace} attribute of \var{p} to \var{newflag} and
  \withsubitem{(file attribute)}{\ttindex{softspace}}returns the
  previous value.  \var{p} does not have to be a file object for this
  function to work properly; any object is supported (thought its only
  interesting if the \member{softspace} attribute can be set).  This
  function clears any errors, and will return \code{0} as the previous
  value if the attribute either does not exist or if there were errors
  in retrieving it.  There is no way to detect errors from this
  function, but doing so should not be needed.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyFile_WriteObject}{PyObject *obj, PyFileObject *p,
                                           int flags}
  Writes object \var{obj} to file object \var{p}.  The only supported
  flag for \var{flags} is
  \constant{Py_PRINT_RAW}\ttindex{Py_PRINT_RAW}; if given, the
  \function{str()} of the object is written instead of the
  \function{repr()}.  Returns \code{0} on success or \code{-1} on
  failure; the appropriate exception will be set.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyFile_WriteString}{const char *s, PyFileObject *p}
  Writes string \var{s} to file object \var{p}.  Returns \code{0} on
  success or \code{-1} on failure; the appropriate exception will be
  set.
\end{cfuncdesc}


\subsection{Instance Objects \label{instanceObjects}}

\obindex{instance}
There are very few functions specific to instance objects.

\begin{cvardesc}{PyTypeObject}{PyInstance_Type}
  Type object for class instances.
\end{cvardesc}

\begin{cfuncdesc}{int}{PyInstance_Check}{PyObject *obj}
  Returns true if \var{obj} is an instance.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyInstance_New}{PyObject *class,
                                             PyObject *arg,
                                             PyObject *kw}
  Create a new instance of a specific class.  The parameters \var{arg}
  and \var{kw} are used as the positional and keyword parameters to
  the object's constructor.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyInstance_NewRaw}{PyObject *class,
                                                PyObject *dict}
  Create a new instance of a specific class without calling it's
  constructor.  \var{class} is the class of new object.  The
  \var{dict} parameter will be used as the object's \member{__dict__};
  if \NULL, a new dictionary will be created for the instance.
\end{cfuncdesc}


\subsection{Method Objects \label{method-objects}}

\obindex{method}
There are some useful functions that are useful for working with
method objects.

\begin{cvardesc}{PyTypeObject}{PyMethod_Type}
  This instance of \ctype{PyTypeObject} represents the Python method
  type.  This is exposed to Python programs as \code{types.MethodType}.
  \withsubitem{(in module types)}{\ttindex{MethodType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyMethod_Check}{PyObject *o}
  Return true if \var{o} is a method object (has type
  \cdata{PyMethod_Type}).  The parameter must not be \NULL.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyMethod_New}{PyObject *func.
                                           PyObject *self, PyObject *class}
  Return a new method object, with \var{func} being any callable
  object; this is the function that will be called when the method is
  called.  If this method should be bound to an instance, \var{self}
  should be the instance and \var{class} should be the class of
  \var{self}, otherwise \var{self} should be \NULL{} and \var{class}
  should be the class which provides the unbound method..
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyMethod_Class}{PyObject *meth}
  Return the class object from which the method \var{meth} was
  created; if this was created from an instance, it will be the class
  of the instance.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyMethod_GET_CLASS}{PyObject *meth}
  Macro version of \cfunction{PyMethod_Class()} which avoids error
  checking.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyMethod_Function}{PyObject *meth}
  Return the function object associated with the method \var{meth}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyMethod_GET_FUNCTION}{PyObject *meth}
  Macro version of \cfunction{PyMethod_Function()} which avoids error
  checking.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyMethod_Self}{PyObject *meth}
  Return the instance associated with the method \var{meth} if it is
  bound, otherwise return \NULL.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyMethod_GET_SELF}{PyObject *meth}
  Macro version of \cfunction{PyMethod_Self()} which avoids error
  checking.
\end{cfuncdesc}


\subsection{Module Objects \label{moduleObjects}}

\obindex{module}
There are only a few functions special to module objects.

\begin{cvardesc}{PyTypeObject}{PyModule_Type}
  This instance of \ctype{PyTypeObject} represents the Python module
  type.  This is exposed to Python programs as
  \code{types.ModuleType}.
  \withsubitem{(in module types)}{\ttindex{ModuleType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyModule_Check}{PyObject *p}
  Returns true if \var{p} is a module object, or a subtype of a module
  object.
  \versionchanged[Allowed subtypes to be accepted]{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyModule_CheckExact}{PyObject *p}
  Returns true if \var{p} is a module object, but not a subtype of
  \cdata{PyModule_Type}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyModule_New}{char *name}
  Return a new module object with the \member{__name__} attribute set
  to \var{name}.  Only the module's \member{__doc__} and
  \member{__name__} attributes are filled in; the caller is
  responsible for providing a \member{__file__} attribute.
  \withsubitem{(module attribute)}{
    \ttindex{__name__}\ttindex{__doc__}\ttindex{__file__}}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyModule_GetDict}{PyObject *module}
  Return the dictionary object that implements \var{module}'s
  namespace; this object is the same as the \member{__dict__}
  attribute of the module object.  This function never fails.
  \withsubitem{(module attribute)}{\ttindex{__dict__}}
  It is recommended extensions use other \cfunction{PyModule_*()}
  and \cfunction{PyObject_*()} functions rather than directly
  manipulate a module's \member{__dict__}.
\end{cfuncdesc}

\begin{cfuncdesc}{char*}{PyModule_GetName}{PyObject *module}
  Return \var{module}'s \member{__name__} value.  If the module does
  not provide one, or if it is not a string, \exception{SystemError}
  is raised and \NULL{} is returned.
  \withsubitem{(module attribute)}{\ttindex{__name__}}
  \withsubitem{(built-in exception)}{\ttindex{SystemError}}
\end{cfuncdesc}

\begin{cfuncdesc}{char*}{PyModule_GetFilename}{PyObject *module}
  Return the name of the file from which \var{module} was loaded using
  \var{module}'s \member{__file__} attribute.  If this is not defined,
  or if it is not a string, raise \exception{SystemError} and return
  \NULL.
  \withsubitem{(module attribute)}{\ttindex{__file__}}
  \withsubitem{(built-in exception)}{\ttindex{SystemError}}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyModule_AddObject}{PyObject *module,
                                           char *name, PyObject *value}
  Add an object to \var{module} as \var{name}.  This is a convenience
  function which can be used from the module's initialization
  function.  This steals a reference to \var{value}.  Returns
  \code{-1} on error, \code{0} on success.
  \versionadded{2.0}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyModule_AddIntConstant}{PyObject *module,
                                                char *name, int value}
  Add an integer constant to \var{module} as \var{name}.  This
  convenience function can be used from the module's initialization
  function. Returns \code{-1} on error, \code{0} on success.
  \versionadded{2.0}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyModule_AddStringConstant}{PyObject *module,
                                                   char *name, char *value}
  Add a string constant to \var{module} as \var{name}.  This
  convenience function can be used from the module's initialization
  function.  The string \var{value} must be null-terminated.  Returns
  \code{-1} on error, \code{0} on success.
  \versionadded{2.0}
\end{cfuncdesc}


\subsection{Iterator Objects \label{iterator-objects}}

Python provides two general-purpose iterator objects.  The first, a
sequence iterator, works with an arbitrary sequence supporting the
\method{__getitem__()} method.  The second works with a callable
object and a sentinel value, calling the callable for each item in the
sequence, and ending the iteration when the sentinel value is
returned.

\begin{cvardesc}{PyTypeObject}{PySeqIter_Type}
  Type object for iterator objects returned by
  \cfunction{PySeqIter_New()} and the one-argument form of the
  \function{iter()} built-in function for built-in sequence types.
  \versionadded{2.2}
\end{cvardesc}

\begin{cfuncdesc}{int}{PySeqIter_Check}{op}
  Return true if the type of \var{op} is \cdata{PySeqIter_Type}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PySeqIter_New}{PyObject *seq}
  Return an iterator that works with a general sequence object,
  \var{seq}.  The iteration ends when the sequence raises
  \exception{IndexError} for the subscripting operation.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cvardesc}{PyTypeObject}{PyCallIter_Type}
  Type object for iterator objects returned by
  \cfunction{PyCallIter_New()} and the two-argument form of the
  \function{iter()} built-in function.
  \versionadded{2.2}
\end{cvardesc}

\begin{cfuncdesc}{int}{PyCallIter_Check}{op}
  Return true if the type of \var{op} is \cdata{PyCallIter_Type}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyCallIter_New}{PyObject *callable,
                                             PyObject *sentinel}
  Return a new iterator.  The first parameter, \var{callable}, can be
  any Python callable object that can be called with no parameters;
  each call to it should return the next item in the iteration.  When
  \var{callable} returns a value equal to \var{sentinel}, the
  iteration will be terminated.
  \versionadded{2.2}
\end{cfuncdesc}


\subsection{Descriptor Objects \label{descriptor-objects}}

``Descriptors'' are objects that describe some attribute of an object.
They are found in the dictionary of type objects.

\begin{cvardesc}{PyTypeObject}{PyProperty_Type}
  The type object for the built-in descriptor types.
  \versionadded{2.2}
\end{cvardesc}

\begin{cfuncdesc}{PyObject*}{PyDescr_NewGetSet}{PyTypeObject *type,
					        PyGetSetDef *getset}
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDescr_NewMember}{PyTypeObject *type,
					        PyMemberDef *meth}
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDescr_NewMethod}{PyTypeObject *type,
                                                PyMethodDef *meth}
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyDescr_NewWrapper}{PyTypeObject *type,
						 struct wrapperbase *wrapper,
                                                 void *wrapped}
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyDescr_IsData}{PyObject *descr}
  Returns true if the descriptor objects \var{descr} describes a data
  attribute, or false if it describes a method.  \var{descr} must be a
  descriptor object; there is no error checking.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyWrapper_New}{PyObject *, PyObject *}
  \versionadded{2.2}
\end{cfuncdesc}


\subsection{Slice Objects \label{slice-objects}}

\begin{cvardesc}{PyTypeObject}{PySlice_Type}
  The type object for slice objects.  This is the same as
  \code{types.SliceType}.
  \withsubitem{(in module types)}{\ttindex{SliceType}}
\end{cvardesc}

\begin{cfuncdesc}{int}{PySlice_Check}{PyObject *ob}
  Returns true if \var{ob} is a slice object; \var{ob} must not be
  \NULL.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PySlice_New}{PyObject *start, PyObject *stop,
                                          PyObject *step}
  Return a new slice object with the given values.  The \var{start},
  \var{stop}, and \var{step} parameters are used as the values of the
  slice object attributes of the same names.  Any of the values may be
  \NULL, in which case the \code{None} will be used for the
  corresponding attribute.  Returns \NULL{} if the new object could
  not be allocated.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PySlice_GetIndices}{PySliceObject *slice, int length,
                                           int *start, int *stop, int *step}
Retrieve the start, stop and step indices from the slice object
\var{slice}, assuming a sequence of length \var{length}. Treats
indices greater than \var{length} as errors.

Returns 0 on success and -1 on error with no exception set (unless one
of the indices was not \constant{None} and failed to be converted to
an integer, in which case -1 is returned with an exception set).

You probably do not want to use this function.  If you want to use
slice objects in versions of Python prior to 2.3, you would probably
do well to incorporate the source of \cfunction{PySlice_GetIndicesEx},
suitably renamed, in the source of your extension.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PySlice_GetIndicesEx}{PySliceObject *slice, int length,
                                             int *start, int *stop, int *step, 
                                             int *slicelength}
Usable replacement for \cfunction{PySlice_GetIndices}.  Retrieve the
start, stop, and step indices from the slice object \var{slice}
assuming a sequence of length \var{length}, and store the length of
the slice in \var{slicelength}.  Out of bounds indices are clipped in
a manner consistent with the handling of normal slices.

Returns 0 on success and -1 on error with exception set.

\versionadded{2.3}
\end{cfuncdesc}


\subsection{Weak Reference Objects \label{weakref-objects}}

Python supports \emph{weak references} as first-class objects.  There
are two specific object types which directly implement weak
references.  The first is a simple reference object, and the second
acts as a proxy for the original object as much as it can.

\begin{cfuncdesc}{int}{PyWeakref_Check}{ob}
  Return true if \var{ob} is either a reference or proxy object.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyWeakref_CheckRef}{ob}
  Return true if \var{ob} is a reference object.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyWeakref_CheckProxy}{ob}
  Return true if \var{ob} is a proxy object.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyWeakref_NewRef}{PyObject *ob,
                                               PyObject *callback}
  Return a weak reference object for the object \var{ob}.  This will
  always return a new reference, but is not guaranteed to create a new
  object; an existing reference object may be returned.  The second
  parameter, \var{callback}, can be a callable object that receives
  notification when \var{ob} is garbage collected; it should accept a
  single paramter, which will be the weak reference object itself.
  \var{callback} may also be \code{None} or \NULL.  If \var{ob}
  is not a weakly-referencable object, or if \var{callback} is not
  callable, \code{None}, or \NULL, this will return \NULL{} and
  raise \exception{TypeError}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyWeakref_NewProxy}{PyObject *ob,
                                                 PyObject *callback}
  Return a weak reference proxy object for the object \var{ob}.  This
  will always return a new reference, but is not guaranteed to create
  a new object; an existing proxy object may be returned.  The second
  parameter, \var{callback}, can be a callable object that receives
  notification when \var{ob} is garbage collected; it should accept a
  single paramter, which will be the weak reference object itself.
  \var{callback} may also be \code{None} or \NULL.  If \var{ob} is not
  a weakly-referencable object, or if \var{callback} is not callable,
  \code{None}, or \NULL, this will return \NULL{} and raise
  \exception{TypeError}.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyWeakref_GetObject}{PyObject *ref}
  Returns the referenced object from a weak reference, \var{ref}.  If
  the referent is no longer live, returns \NULL.
  \versionadded{2.2}
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyWeakref_GET_OBJECT}{PyObject *ref}
  Similar to \cfunction{PyWeakref_GetObject()}, but implemented as a
  macro that does no error checking.
  \versionadded{2.2}
\end{cfuncdesc}


\subsection{CObjects \label{cObjects}}

\obindex{CObject}
Refer to \emph{Extending and Embedding the Python Interpreter},
section~1.12, ``Providing a C API for an Extension Module,'' for more
information on using these objects.


\begin{ctypedesc}{PyCObject}
  This subtype of \ctype{PyObject} represents an opaque value, useful
  for C extension modules who need to pass an opaque value (as a
  \ctype{void*} pointer) through Python code to other C code.  It is
  often used to make a C function pointer defined in one module
  available to other modules, so the regular import mechanism can be
  used to access C APIs defined in dynamically loaded modules.
\end{ctypedesc}

\begin{cfuncdesc}{int}{PyCObject_Check}{PyObject *p}
  Returns true if its argument is a \ctype{PyCObject}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyCObject_FromVoidPtr}{void* cobj,
                                                    void (*destr)(void *)}
  Creates a \ctype{PyCObject} from the \code{void *}\var{cobj}.  The
  \var{destr} function will be called when the object is reclaimed,
  unless it is \NULL.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyCObject_FromVoidPtrAndDesc}{void* cobj,
	                          void* desc, void (*destr)(void *, void *)}
  Creates a \ctype{PyCObject} from the \ctype{void *}\var{cobj}.  The
  \var{destr} function will be called when the object is reclaimed.
  The \var{desc} argument can be used to pass extra callback data for
  the destructor function.
\end{cfuncdesc}

\begin{cfuncdesc}{void*}{PyCObject_AsVoidPtr}{PyObject* self}
  Returns the object \ctype{void *} that the \ctype{PyCObject}
  \var{self} was created with.
\end{cfuncdesc}

\begin{cfuncdesc}{void*}{PyCObject_GetDesc}{PyObject* self}
  Returns the description \ctype{void *} that the \ctype{PyCObject}
  \var{self} was created with.
\end{cfuncdesc}


\subsection{Cell Objects \label{cell-objects}}

``Cell'' objects are used to implement variables referenced by
multiple scopes.  For each such variable, a cell object is created to
store the value; the local variables of each stack frame that
references the value contains a reference to the cells from outer
scopes which also use that variable.  When the value is accessed, the
value contained in the cell is used instead of the cell object
itself.  This de-referencing of the cell object requires support from
the generated byte-code; these are not automatically de-referenced
when accessed.  Cell objects are not likely to be useful elsewhere.

\begin{ctypedesc}{PyCellObject}
  The C structure used for cell objects.
\end{ctypedesc}

\begin{cvardesc}{PyTypeObject}{PyCell_Type}
  The type object corresponding to cell objects
\end{cvardesc}

\begin{cfuncdesc}{int}{PyCell_Check}{ob}
  Return true if \var{ob} is a cell object; \var{ob} must not be
  \NULL.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyCell_New}{PyObject *ob}
  Create and return a new cell object containing the value \var{ob}.
  The parameter may be \NULL.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyCell_Get}{PyObject *cell}
  Return the contents of the cell \var{cell}.
\end{cfuncdesc}

\begin{cfuncdesc}{PyObject*}{PyCell_GET}{PyObject *cell}
  Return the contents of the cell \var{cell}, but without checking
  that \var{cell} is non-\NULL{} and a call object.
\end{cfuncdesc}

\begin{cfuncdesc}{int}{PyCell_Set}{PyObject *cell, PyObject *value}
  Set the contents of the cell object \var{cell} to \var{value}.  This
  releases the reference to any current content of the cell.
  \var{value} may be \NULL.  \var{cell} must be non-\NULL; if it is
  not a cell object, \code{-1} will be returned.  On success, \code{0}
  will be returned.
\end{cfuncdesc}

\begin{cfuncdesc}{void}{PyCell_SET}{PyObject *cell, PyObject *value}
  Sets the value of the cell object \var{cell} to \var{value}.  No
  reference counts are adjusted, and no checks are made for safety;
  \var{cell} must be non-\NULL{} and must be a cell object.
\end{cfuncdesc}