| \section{Built-in Functions} |
| \label{built-in-funcs} |
| |
| The Python interpreter has a number of functions built into it that |
| are always available. They are listed here in alphabetical order. |
| |
| |
| \renewcommand{\indexsubitem}{(built-in function)} |
| |
| \begin{funcdesc}{__import__}{name\optional{, globals\optional{, locals\optional{, fromlist}}}} |
| This function is invoked by the \code{import} statement. It |
| mainly exists so that you can replace it with another |
| function that has a compatible interface, in order to change the |
| semantics of the \code{import} statement. For examples of why and |
| how you would do this, see the standard library modules \code{ni}, |
| \code{ihooks} and \code{rexec}. See also the built-in module |
| \code{imp}, which defines some useful operations out of which you can |
| build your own \code{__import__()} function. |
| \stindex{import} |
| \refstmodindex{ni} |
| \refstmodindex{ihooks} |
| \refstmodindex{rexec} |
| \refbimodindex{imp} |
| |
| For example, the statement \code{import spam} results in the following |
| call: |
| \code{__import__('spam', globals(), locals(), [])}; |
| the statement \code{from spam.ham import eggs} results in |
| \code{__import__('spam.ham', globals(), locals(), ['eggs'])}. |
| Note that even though \code{locals()} and \code{['eggs']} are passed |
| in as arguments, the \code{__import__()} function does not set the |
| local variable named \code{eggs}; this is done by subsequent code that |
| is generated for the import statement. (In fact, the standard |
| implementation does not use its \var{locals} argument at all, and uses |
| its \var{globals} only to determine the package context of the |
| \code{import} statement.) |
| |
| When the \var{name} variable is of the form \code{package.module}, |
| normally, the top-level package (the name up till the first dot) is |
| returned, \emph{not} the module named by \var{name}. However, when a |
| non-empty \var{fromlist} argument is given, the module named by |
| \var{name} is returned. This is done for compatibility with the |
| bytecode generated for the different kinds of import statement; when |
| using \code{import spam.ham.eggs}, the top-level package \code{spam} |
| must be placed in the importing namespace, but when using \code{from |
| spam.ham import eggs}, the \code{spam.ham} subpackage must be used to |
| find the \code{eggs} variable. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{abs}{x} |
| Return the absolute value of a number. The argument may be a plain |
| or long integer or a floating point number. If the argument is a |
| complex number, its magnitude is returned. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{apply}{function\, args\optional{, keywords}} |
| The \var{function} argument must be a callable object (a user-defined or |
| built-in function or method, or a class object) and the \var{args} |
| argument must be a tuple. The \var{function} is called with |
| \var{args} as argument list; the number of arguments is the the length |
| of the tuple. (This is different from just calling |
| \code{\var{func}(\var{args})}, since in that case there is always |
| exactly one argument.) |
| If the optional \var{keywords} argument is present, it must be a |
| dictionary whose keys are strings. It specifies keyword arguments to |
| be added to the end of the the argument list. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{callable}{object} |
| Return true if the \var{object} argument appears callable, false if |
| not. If this returns true, it is still possible that a call fails, |
| but if it is false, calling \var{object} will never succeed. Note |
| that classes are callable (calling a class returns a new instance); |
| class instances are callable if they have an attribute \code{__call__}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{chr}{i} |
| Return a string of one character whose \ASCII{} code is the integer |
| \var{i}, e.g., \code{chr(97)} returns the string \code{'a'}. This is the |
| inverse of \code{ord()}. The argument must be in the range [0..255], |
| inclusive. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{cmp}{x\, y} |
| Compare the two objects \var{x} and \var{y} and return an integer |
| according to the outcome. The return value is negative if \code{\var{x} |
| < \var{y}}, zero if \code{\var{x} == \var{y}} and strictly positive if |
| \code{\var{x} > \var{y}}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{coerce}{x\, y} |
| Return a tuple consisting of the two numeric arguments converted to |
| a common type, using the same rules as used by arithmetic |
| operations. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{compile}{string\, filename\, kind} |
| Compile the \var{string} into a code object. Code objects can be |
| executed by an \code{exec} statement or evaluated by a call to |
| \code{eval()}. The \var{filename} argument should |
| give the file from which the code was read; pass e.g. \code{'<string>'} |
| if it wasn't read from a file. The \var{kind} argument specifies |
| what kind of code must be compiled; it can be \code{'exec'} if |
| \var{string} consists of a sequence of statements, \code{'eval'} |
| if it consists of a single expression, or \code{'single'} if |
| it consists of a single interactive statement (in the latter case, |
| expression statements that evaluate to something else than |
| \code{None} will printed). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{complex}{real\optional{, imag}} |
| Create a complex number with the value \var{real} + \var{imag}*j. |
| Each argument may be any numeric type (including complex). |
| If \var{imag} is omitted, it defaults to zero and the function |
| serves as a numeric conversion function like \code{int}, \code{long} |
| and \code{float}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{delattr}{object\, name} |
| This is a relative of \code{setattr}. The arguments are an |
| object and a string. The string must be the name |
| of one of the object's attributes. The function deletes |
| the named attribute, provided the object allows it. For example, |
| \code{delattr(\var{x}, '\var{foobar}')} is equivalent to |
| \code{del \var{x}.\var{foobar}}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{dir}{} |
| Without arguments, return the list of names in the current local |
| symbol table. With an argument, attempts to return a list of valid |
| attribute for that object. This information is gleaned from the |
| object's \code{__dict__}, \code{__methods__} and \code{__members__} |
| attributes, if defined. The list is not necessarily complete; e.g., |
| for classes, attributes defined in base classes are not included, |
| and for class instances, methods are not included. |
| The resulting list is sorted alphabetically. For example: |
| |
| \bcode\begin{verbatim} |
| >>> import sys |
| >>> dir() |
| ['sys'] |
| >>> dir(sys) |
| ['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout'] |
| >>> |
| \end{verbatim}\ecode |
| \end{funcdesc} |
| |
| \begin{funcdesc}{divmod}{a\, b} |
| Take two numbers as arguments and return a pair of numbers consisting |
| of their quotient and remainder when using long division. With mixed |
| operand types, the rules for binary arithmetic operators apply. For |
| plain and long integers, the result is the same as |
| \code{(\var{a} / \var{b}, \var{a} \%{} \var{b})}. |
| For floating point numbers the result is the same as |
| \code{(math.floor(\var{a} / \var{b}), \var{a} \%{} \var{b})}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{eval}{expression\optional{\, globals\optional{\, locals}}} |
| The arguments are a string and two optional dictionaries. The |
| \var{expression} argument is parsed and evaluated as a Python |
| expression (technically speaking, a condition list) using the |
| \var{globals} and \var{locals} dictionaries as global and local name |
| space. If the \var{locals} dictionary is omitted it defaults to |
| the \var{globals} dictionary. If both dictionaries are omitted, the |
| expression is executed in the environment where \code{eval} is |
| called. The return value is the result of the evaluated expression. |
| Syntax errors are reported as exceptions. Example: |
| |
| \bcode\begin{verbatim} |
| >>> x = 1 |
| >>> print eval('x+1') |
| 2 |
| >>> |
| \end{verbatim}\ecode |
| % |
| This function can also be used to execute arbitrary code objects |
| (e.g.\ created by \code{compile()}). In this case pass a code |
| object instead of a string. The code object must have been compiled |
| passing \code{'eval'} to the \var{kind} argument. |
| |
| Hints: dynamic execution of statements is supported by the |
| \code{exec} statement. Execution of statements from a file is |
| supported by the \code{execfile()} function. The \code{globals()} |
| and \code{locals()} functions returns the current global and local |
| dictionary, respectively, which may be useful |
| to pass around for use by \code{eval()} or \code{execfile()}. |
| |
| \end{funcdesc} |
| |
| \begin{funcdesc}{execfile}{file\optional{\, globals\optional{\, locals}}} |
| This function is similar to the |
| \code{exec} statement, but parses a file instead of a string. It is |
| different from the \code{import} statement in that it does not use |
| the module administration --- it reads the file unconditionally and |
| does not create a new module.\footnote{It is used relatively rarely |
| so does not warrant being made into a statement.} |
| |
| The arguments are a file name and two optional dictionaries. The |
| file is parsed and evaluated as a sequence of Python statements |
| (similarly to a module) using the \var{globals} and \var{locals} |
| dictionaries as global and local name space. If the \var{locals} |
| dictionary is omitted it defaults to the \var{globals} dictionary. |
| If both dictionaries are omitted, the expression is executed in the |
| environment where \code{execfile()} is called. The return value is |
| \code{None}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{filter}{function\, list} |
| Construct a list from those elements of \var{list} for which |
| \var{function} returns true. If \var{list} is a string or a tuple, |
| the result also has that type; otherwise it is always a list. If |
| \var{function} is \code{None}, the identity function is assumed, |
| i.e.\ all elements of \var{list} that are false (zero or empty) are |
| removed. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{float}{x} |
| Convert a string or a number to floating point. If the argument is a |
| string, it must contain a possibly singed decimal or floating point |
| number, possibly embedded in whitespace; |
| this behaves identical to \code{string.atof(\var{x})}. |
| Otherwise, the argument may be a plain or |
| long integer or a floating point number, and a floating point number |
| with the same value (within Python's floating point precision) is |
| returned. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{getattr}{object\, name} |
| The arguments are an object and a string. The string must be the |
| name |
| of one of the object's attributes. The result is the value of that |
| attribute. For example, \code{getattr(\var{x}, '\var{foobar}')} is equivalent to |
| \code{\var{x}.\var{foobar}}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{globals}{} |
| Return a dictionary representing the current global symbol table. |
| This is always the dictionary of the current module (inside a |
| function or method, this is the module where it is defined, not the |
| module from which it is called). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{hasattr}{object\, name} |
| The arguments are an object and a string. The result is 1 if the |
| string is the name of one of the object's attributes, 0 if not. |
| (This is implemented by calling \code{getattr(object, name)} and |
| seeing whether it raises an exception or not.) |
| \end{funcdesc} |
| |
| \begin{funcdesc}{hash}{object} |
| Return the hash value of the object (if it has one). Hash values |
| are integers. They are used to quickly compare dictionary |
| keys during a dictionary lookup. Numeric values that compare equal |
| have the same hash value (even if they are of different types, e.g. |
| 1 and 1.0). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{hex}{x} |
| Convert an integer number (of any size) to a hexadecimal string. |
| The result is a valid Python expression. Note: this always yields |
| an unsigned literal, e.g. on a 32-bit machine, \code{hex(-1)} yields |
| \code{'0xffffffff'}. When evaluated on a machine with the same |
| word size, this literal is evaluated as -1; at a different word |
| size, it may turn up as a large positive number or raise an |
| \code{OverflowError} exception. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{id}{object} |
| Return the `identity' of an object. This is an integer which is |
| guaranteed to be unique and constant for this object during its |
| lifetime. (Two objects whose lifetimes are disjunct may have the |
| same id() value.) (Implementation note: this is the address of the |
| object.) |
| \end{funcdesc} |
| |
| \begin{funcdesc}{input}{\optional{prompt}} |
| Almost equivalent to \code{eval(raw_input(\var{prompt}))}. Like |
| \code{raw_input()}, the \var{prompt} argument is optional, and the |
| \code{readline} module is used when loaded. The difference |
| is that a long input expression may be broken over multiple lines using |
| the backslash convention. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{intern}{string} |
| Enter \var{string} in the table of ``interned'' strings and return |
| the interned string -- which is \var{string} itself or a copy. |
| Interning strings is useful to gain a little performance on |
| dictionary lookup -- if the keys in a dictionary are interned, and |
| the lookup key is interned, the key comparisons (after hashing) can |
| be done by a pointer compare instead of a string compare. Normally, |
| the names used in Python programs are automatically interned, and |
| the dictionaries used to hold module, class or instance attributes |
| have interned keys. Interned strings are immortal (i.e. never get |
| garbage collected). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{int}{x} |
| Convert a string or number to a plain integer. If the argument is a |
| string, it must contain a possibly singed decimal number |
| representable as a Python integer, possibly embedded in whitespace; |
| this behaves identical to \code{string.atoi(\var{x})}. |
| Otherwise, the argument may be a plain or |
| long integer or a floating point number. Conversion of floating |
| point numbers to integers is defined by the C semantics; normally |
| the conversion truncates towards zero.\footnote{This is ugly --- the |
| language definition should require truncation towards zero.} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{isinstance}{object, class} |
| Return true if the \var{object} argument is an instance of the |
| \var{class} argument, or of a (direct or indirect) subclass thereof. |
| Also return true if \var{class} is a type object and \var{object} is |
| an object of that type. If \var{object} is not a class instance or a |
| object of the given type, the function always returns false. If |
| \var{class} is neither a class object nor a type object, a |
| \code{TypeError} exception is raised. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{issubclass}{class1, class2} |
| Return true if \var{class1} is a subclass (direct or indirect) of |
| \var{class2}. A class is considered a subclass of itself. If either |
| argument is not a class object, a \code{TypeError} exception is raised. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{len}{s} |
| Return the length (the number of items) of an object. The argument |
| may be a sequence (string, tuple or list) or a mapping (dictionary). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{list}{sequence} |
| Return a list whose items are the same and in the same order as |
| \var{sequence}'s items. If \var{sequence} is already a list, |
| a copy is made and returned, similar to \code{\var{sequence}[:]}. |
| For instance, \code{list('abc')} returns |
| returns \code{['a', 'b', 'c']} and \code{list( (1, 2, 3) )} returns |
| \code{[1, 2, 3]}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{locals}{} |
| Return a dictionary representing the current local symbol table. |
| Inside a function, modifying this dictionary does not always have the |
| desired effect. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{long}{x} |
| Convert a string or number to a long integer. If the argument is a |
| string, it must contain a possibly singed decimal number of |
| arbitrary size, possibly embedded in whitespace; |
| this behaves identical to \code{string.atol(\var{x})}. |
| Otherwise, the argument may be a plain or |
| long integer or a floating point number, and a long integer with |
| the same value is returned. Conversion of floating |
| point numbers to integers is defined by the C semantics; |
| see the description of \code{int()}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{map}{function\, list\, ...} |
| Apply \var{function} to every item of \var{list} and return a list |
| of the results. If additional \var{list} arguments are passed, |
| \var{function} must take that many arguments and is applied to |
| the items of all lists in parallel; if a list is shorter than another |
| it is assumed to be extended with \code{None} items. If |
| \var{function} is \code{None}, the identity function is assumed; if |
| there are multiple list arguments, \code{map} returns a list |
| consisting of tuples containing the corresponding items from all lists |
| (i.e. a kind of transpose operation). The \var{list} arguments may be |
| any kind of sequence; the result is always a list. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{max}{s} |
| Return the largest item of a non-empty sequence (string, tuple or |
| list). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{min}{s} |
| Return the smallest item of a non-empty sequence (string, tuple or |
| list). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{oct}{x} |
| Convert an integer number (of any size) to an octal string. The |
| result is a valid Python expression. Note: this always yields |
| an unsigned literal, e.g. on a 32-bit machine, \code{oct(-1)} yields |
| \code{'037777777777'}. When evaluated on a machine with the same |
| word size, this literal is evaluated as -1; at a different word |
| size, it may turn up as a large positive number or raise an |
| \code{OverflowError} exception. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{open}{filename\optional{\, mode\optional{\, bufsize}}} |
| Return a new file object (described earlier under Built-in Types). |
| The first two arguments are the same as for \code{stdio}'s |
| \code{fopen()}: \var{filename} is the file name to be opened, |
| \var{mode} indicates how the file is to be opened: \code{'r'} for |
| reading, \code{'w'} for writing (truncating an existing file), and |
| \code{'a'} opens it for appending (which on {\em some} \UNIX{} |
| systems means that {\em all} writes append to the end of the file, |
| regardless of the current seek position). |
| Modes \code{'r+'}, \code{'w+'} and |
| \code{'a+'} open the file for updating, provided the underlying |
| \code{stdio} library understands this. On systems that differentiate |
| between binary and text files, \code{'b'} appended to the mode opens |
| the file in binary mode. If the file cannot be opened, \code{IOError} |
| is raised. |
| If \var{mode} is omitted, it defaults to \code{'r'}. |
| The optional \var{bufsize} argument specifies the file's desired |
| buffer size: 0 means unbuffered, 1 means line buffered, any other |
| positive value means use a buffer of (approximately) that size. A |
| negative \var{bufsize} means to use the system default, which is |
| usually line buffered for for tty devices and fully buffered for other |
| files.% |
| \footnote{Specifying a buffer size currently has no effect on systems |
| that don't have \code{setvbuf()}. The interface to specify the buffer |
| size is not done using a method that calls \code{setvbuf()}, because |
| that may dump core when called after any I/O has been performed, and |
| there's no reliable way to determine whether this is the case.} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{ord}{c} |
| Return the \ASCII{} value of a string of one character. E.g., |
| \code{ord('a')} returns the integer \code{97}. This is the inverse of |
| \code{chr()}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{pow}{x\, y\optional{\, z}} |
| Return \var{x} to the power \var{y}; if \var{z} is present, return |
| \var{x} to the power \var{y}, modulo \var{z} (computed more |
| efficiently than \code{pow(\var{x}, \var{y}) \% \var{z}}). |
| The arguments must have |
| numeric types. With mixed operand types, the rules for binary |
| arithmetic operators apply. The effective operand type is also the |
| type of the result; if the result is not expressible in this type, the |
| function raises an exception; e.g., \code{pow(2, -1)} or \code{pow(2, |
| 35000)} is not allowed. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{range}{\optional{start\,} stop\optional{\, step}} |
| This is a versatile function to create lists containing arithmetic |
| progressions. It is most often used in \code{for} loops. The |
| arguments must be plain integers. If the \var{step} argument is |
| omitted, it defaults to \code{1}. If the \var{start} argument is |
| omitted, it defaults to \code{0}. The full form returns a list of |
| plain integers \code{[\var{start}, \var{start} + \var{step}, |
| \var{start} + 2 * \var{step}, \ldots]}. If \var{step} is positive, |
| the last element is the largest \code{\var{start} + \var{i} * |
| \var{step}} less than \var{stop}; if \var{step} is negative, the last |
| element is the largest \code{\var{start} + \var{i} * \var{step}} |
| greater than \var{stop}. \var{step} must not be zero (or else an |
| exception is raised). Example: |
| |
| \bcode\begin{verbatim} |
| >>> range(10) |
| [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] |
| >>> range(1, 11) |
| [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] |
| >>> range(0, 30, 5) |
| [0, 5, 10, 15, 20, 25] |
| >>> range(0, 10, 3) |
| [0, 3, 6, 9] |
| >>> range(0, -10, -1) |
| [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] |
| >>> range(0) |
| [] |
| >>> range(1, 0) |
| [] |
| >>> |
| \end{verbatim}\ecode |
| \end{funcdesc} |
| |
| \begin{funcdesc}{raw_input}{\optional{prompt}} |
| If the \var{prompt} argument is present, it is written to standard output |
| without a trailing newline. The function then reads a line from input, |
| converts it to a string (stripping a trailing newline), and returns that. |
| When \EOF{} is read, \code{EOFError} is raised. Example: |
| |
| \bcode\begin{verbatim} |
| >>> s = raw_input('--> ') |
| --> Monty Python's Flying Circus |
| >>> s |
| "Monty Python's Flying Circus" |
| >>> |
| \end{verbatim}\ecode |
| |
| If the \code{readline} module was loaded, then |
| \code{raw_input()} will use it to provide elaborate |
| line editing and history features. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{reduce}{function\, list\optional{\, initializer}} |
| Apply the binary \var{function} to the items of \var{list} so as to |
| reduce the list to a single value. E.g., |
| \code{reduce(lambda x, y: x*y, \var{list}, 1)} returns the product of |
| the elements of \var{list}. The optional \var{initializer} can be |
| thought of as being prepended to \var{list} so as to allow reduction |
| of an empty \var{list}. The \var{list} arguments may be any kind of |
| sequence. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{reload}{module} |
| Re-parse and re-initialize an already imported \var{module}. The |
| argument must be a module object, so it must have been successfully |
| imported before. This is useful if you have edited the module source |
| file using an external editor and want to try out the new version |
| without leaving the Python interpreter. The return value is the |
| module object (i.e.\ the same as the \var{module} argument). |
| |
| There are a number of caveats: |
| |
| If a module is syntactically correct but its initialization fails, the |
| first \code{import} statement for it does not bind its name locally, |
| but does store a (partially initialized) module object in |
| \code{sys.modules}. To reload the module you must first |
| \code{import} it again (this will bind the name to the partially |
| initialized module object) before you can \code{reload()} it. |
| |
| When a module is reloaded, its dictionary (containing the module's |
| global variables) is retained. Redefinitions of names will override |
| the old definitions, so this is generally not a problem. If the new |
| version of a module does not define a name that was defined by the old |
| version, the old definition remains. This feature can be used to the |
| module's advantage if it maintains a global table or cache of objects |
| --- with a \code{try} statement it can test for the table's presence |
| and skip its initialization if desired. |
| |
| It is legal though generally not very useful to reload built-in or |
| dynamically loaded modules, except for \code{sys}, \code{__main__} and |
| \code{__builtin__}. In certain cases, however, extension modules are |
| not designed to be initialized more than once, and may fail in |
| arbitrary ways when reloaded. |
| |
| If a module imports objects from another module using \code{from} |
| \ldots{} \code{import} \ldots{}, calling \code{reload()} for the other |
| module does not redefine the objects imported from it --- one way |
| around this is to re-execute the \code{from} statement, another is to |
| use \code{import} and qualified names (\var{module}.\var{name}) |
| instead. |
| |
| If a module instantiates instances of a class, reloading the module |
| that defines the class does not affect the method definitions of the |
| instances --- they continue to use the old class definition. The same |
| is true for derived classes. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{repr}{object} |
| Return a string containing a printable representation of an object. |
| This is the same value yielded by conversions (reverse quotes). |
| It is sometimes useful to be able to access this operation as an |
| ordinary function. For many types, this function makes an attempt |
| to return a string that would yield an object with the same value |
| when passed to \code{eval()}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{round}{x\, n} |
| Return the floating point value \var{x} rounded to \var{n} digits |
| after the decimal point. If \var{n} is omitted, it defaults to zero. |
| The result is a floating point number. Values are rounded to the |
| closest multiple of 10 to the power minus \var{n}; if two multiples |
| are equally close, rounding is done away from 0 (so e.g. |
| \code{round(0.5)} is \code{1.0} and \code{round(-0.5)} is \code{-1.0}). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{setattr}{object\, name\, value} |
| This is the counterpart of \code{getattr}. The arguments are an |
| object, a string and an arbitrary value. The string must be the name |
| of one of the object's attributes. The function assigns the value to |
| the attribute, provided the object allows it. For example, |
| \code{setattr(\var{x}, '\var{foobar}', 123)} is equivalent to |
| \code{\var{x}.\var{foobar} = 123}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{slice}{\optional{start\,} stop\optional{\, step}} |
| Return a slice object representing the set of indices specified by |
| \code{range(\var{start}, \var{stop}, \var{step})}. The \var{start} |
| and \var{step} arguments default to None. Slice objects have |
| read-only data attributes \code{start}, \code{stop} and \code{step} |
| which merely return the argument values (or their default). They have |
| no other explicit functionality; however they are used by Numerical |
| Python and other third party extensions. Slice objects are also |
| generated when extended indexing syntax is used, e.g. for |
| \code{a[start:stop:step]} or \code{a[start:stop, i]}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{str}{object} |
| Return a string containing a nicely printable representation of an |
| object. For strings, this returns the string itself. The difference |
| with \code{repr(\var{object})} is that \code{str(\var{object})} does not |
| always attempt to return a string that is acceptable to \code{eval()}; |
| its goal is to return a printable string. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{tuple}{sequence} |
| Return a tuple whose items are the same and in the same order as |
| \var{sequence}'s items. If \var{sequence} is already a tuple, it |
| is returned unchanged. For instance, \code{tuple('abc')} returns |
| returns \code{('a', 'b', 'c')} and \code{tuple([1, 2, 3])} returns |
| \code{(1, 2, 3)}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{type}{object} |
| Return the type of an \var{object}. The return value is a type |
| object. The standard module \code{types} defines names for all |
| built-in types. |
| \refstmodindex{types} |
| \obindex{type} |
| For instance: |
| |
| \bcode\begin{verbatim} |
| >>> import types |
| >>> if isinstance(x, types.StringType): print "It's a string" |
| \end{verbatim}\ecode |
| \end{funcdesc} |
| |
| \begin{funcdesc}{vars}{\optional{object}} |
| Without arguments, return a dictionary corresponding to the current |
| local symbol table. With a module, class or class instance object as |
| argument (or anything else that has a \code{__dict__} attribute), |
| returns a dictionary corresponding to the object's symbol table. |
| The returned dictionary should not be modified: the effects on the |
| corresponding symbol table are undefined.% |
| \footnote{In the current implementation, local variable bindings |
| cannot normally be affected this way, but variables retrieved from |
| other scopes (e.g. modules) can be. This may change.} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{xrange}{\optional{start\,} stop\optional{\, step}} |
| This function is very similar to \code{range()}, but returns an |
| ``xrange object'' instead of a list. This is an opaque sequence type |
| which yields the same values as the corresponding list, without |
| actually storing them all simultaneously. The advantage of |
| \code{xrange()} over \code{range()} is minimal (since \code{xrange()} |
| still has to create the values when asked for them) except when a very |
| large range is used on a memory-starved machine (e.g. MS-DOS) or when all |
| of the range's elements are never used (e.g. when the loop is usually |
| terminated with \code{break}). |
| \end{funcdesc} |