Doc/lib/liboperator.tex

\section{\module{operator} ---
         Standard operators as functions.}
\declaremodule{builtin}{operator}
\sectionauthor{Skip Montanaro}{skip@automatrix.com}

\modulesynopsis{All Python's standard operators as built-in functions.}


The \module{operator} module exports a set of functions implemented in C
corresponding to the intrinsic operators of Python.  For example,
\code{operator.add(x, y)} is equivalent to the expression \code{x+y}.  The
function names are those used for special class methods; variants without
leading and trailing \samp{__} are also provided for convenience.

The \module{operator} module defines the following functions:

\begin{funcdesc}{add}{a, b}
\funcline{__add__}{a, b}
Return \var{a} \code{+} \var{b}, for \var{a} and \var{b} numbers.
\end{funcdesc}

\begin{funcdesc}{sub}{a, b}
\funcline{__sub__}{a, b}
Return \var{a} \code{-} \var{b}.
\end{funcdesc}

\begin{funcdesc}{mul}{a, b}
\funcline{__mul__}{a, b}
Return \var{a} \code{*} \var{b}, for \var{a} and \var{b} numbers.
\end{funcdesc}

\begin{funcdesc}{div}{a, b}
\funcline{__div__}{a, b}
Return \var{a} \code{/} \var{b}.
\end{funcdesc}

\begin{funcdesc}{mod}{a, b}
\funcline{__mod__}{a, b}
Return \var{a} \code{\%} \var{b}.
\end{funcdesc}

\begin{funcdesc}{neg}{o}
\funcline{__neg__}{o}
Return \var{o} negated.
\end{funcdesc}

\begin{funcdesc}{pos}{o}
\funcline{__pos__}{o}
Return \var{o} positive.
\end{funcdesc}

\begin{funcdesc}{abs}{o}
\funcline{__abs__}{o}
Return the absolute value of \var{o}.
\end{funcdesc}

\begin{funcdesc}{inv}{o}
\funcline{invert}{o}
\funcline{__inv__}{o}
\funcline{__invert__}{o}
Return the inverse of \var{o}.  The names \function{invert()} and
\function{__invert__()} were added in Python 2.0.
\end{funcdesc}

\begin{funcdesc}{lshift}{a, b}
\funcline{__lshift__}{a, b}
Return \var{a} shifted left by \var{b}.
\end{funcdesc}

\begin{funcdesc}{rshift}{a, b}
\funcline{__rshift__}{a, b}
Return \var{a} shifted right by \var{b}.
\end{funcdesc}

\begin{funcdesc}{and_}{a, b}
\funcline{__and__}{a, b}
Return the bitwise and of \var{a} and \var{b}.
\end{funcdesc}

\begin{funcdesc}{or_}{a, b}
\funcline{__or__}{a, b}
Return the bitwise or of \var{a} and \var{b}.
\end{funcdesc}

\begin{funcdesc}{xor}{a, b}
\funcline{__xor__}{a, b}
Return the bitwise exclusive or of \var{a} and \var{b}.
\end{funcdesc}

\begin{funcdesc}{not_}{o}
\funcline{__not__}{o}
Return the outcome of \keyword{not} \var{o}.  (Note that there is no
\method{__not__()} method for object instances; only the interpreter
core defines this operation.)
\end{funcdesc}

\begin{funcdesc}{truth}{o}
Return \code{1} if \var{o} is true, and 0 otherwise.
\end{funcdesc}

\begin{funcdesc}{concat}{a, b}
\funcline{__concat__}{a, b}
Return \var{a} \code{+} \var{b} for \var{a} and \var{b} sequences.
\end{funcdesc}

\begin{funcdesc}{repeat}{a, b}
\funcline{__repeat__}{a, b}
Return \var{a} \code{*} \var{b} where \var{a} is a sequence and
\var{b} is an integer.
\end{funcdesc}

\begin{funcdesc}{contains}{a, b}
\funcline{__contains__}{a, b}
Return the outcome of the test \var{b} \code{in} \var{a}.
Note the reversed operands.  The name \function{__contains__()} was
added in Python 2.0.
\end{funcdesc}

\begin{funcdesc}{sequenceIncludes}{\unspecified}
\deprecated{2.0}{Use \function{contains()} instead.}
Alias for \function{contains()}.
\end{funcdesc}

\begin{funcdesc}{countOf}{a, b}
Return the number of occurrences of \var{b} in \var{a}.
\end{funcdesc}

\begin{funcdesc}{indexOf}{a, b}
Return the index of the first of occurrence of \var{b} in \var{a}.
\end{funcdesc}

\begin{funcdesc}{getitem}{a, b}
\funcline{__getitem__}{a, b}
Return the value of \var{a} at index \var{b}.
\end{funcdesc}

\begin{funcdesc}{setitem}{a, b, c}
\funcline{__setitem__}{a, b, c}
Set the value of \var{a} at index \var{b} to \var{c}.
\end{funcdesc}

\begin{funcdesc}{delitem}{a, b}
\funcline{__delitem__}{a, b}
Remove the value of \var{a} at index \var{b}.
\end{funcdesc}

\begin{funcdesc}{getslice}{a, b, c}
\funcline{__getslice__}{a, b, c}
Return the slice of \var{a} from index \var{b} to index \var{c}\code{-1}.
\end{funcdesc}

\begin{funcdesc}{setslice}{a, b, c, v}
\funcline{__setslice__}{a, b, c, v}
Set the slice of \var{a} from index \var{b} to index \var{c}\code{-1} to the
sequence \var{v}.
\end{funcdesc}

\begin{funcdesc}{delslice}{a, b, c}
\funcline{__delslice__}{a, b, c}
Delete the slice of \var{a} from index \var{b} to index \var{c}\code{-1}.
\end{funcdesc}

The \module{operator} also defines a few predicates to test the type
of objects.  \strong{Note:}  Be careful not to misinterpret the
results of these functions; only \function{isCallable()} has any
measure of reliability with instance objects.  For example:

\begin{verbatim}
>>> class C:
...     pass
... 
>>> import operator
>>> o = C()
>>> operator.isMappingType(o)
1
\end{verbatim}

\begin{funcdesc}{isCallable}{o}
\deprecated{2.0}{Use the \function{callable()} built-in function instead.}
Returns true if the object \var{o} can be called like a function,
otherwise it returns false.  True is returned for functions, bound and
unbound methods, class objects, and instance objects which support the
\method{__call__()} method.
\end{funcdesc}

\begin{funcdesc}{isMappingType}{o}
Returns true if the object \var{o} supports the mapping interface.
This is true for dictionaries and all instance objects.
\strong{Warning:} There is no reliable way to test if an instance
supports the complete mapping protocol since the interface itself is
ill-defined.  This makes this test less useful than it otherwise might
be.
\end{funcdesc}

\begin{funcdesc}{isNumberType}{o}
Returns true if the object \var{o} represents a number.  This is true
for all numeric types implemented in C, and for all instance objects.
\strong{Warning:}  There is no reliable way to test if an instance
supports the complete numeric interface since the interface itself is
ill-defined.  This makes this test less useful than it otherwise might
be.
\end{funcdesc}

\begin{funcdesc}{isSequenceType}{o}
Returns true if the object \var{o} supports the sequence protocol.
This returns true for all objects which define sequence methods in C,
and for all instance objects.  \strong{Warning:} There is no reliable
way to test if an instance supports the complete sequence interface
since the interface itself is ill-defined.  This makes this test less
useful than it otherwise might be.
\end{funcdesc}


Example: Build a dictionary that maps the ordinals from \code{0} to
\code{256} to their character equivalents.

\begin{verbatim}
>>> import operator
>>> d = {}
>>> keys = range(256)
>>> vals = map(chr, keys)
>>> map(operator.setitem, [d]*len(keys), keys, vals)
\end{verbatim}


\subsection{Mapping Operators to Functions \label{operator-map}}

This table shows how abstract operations correspond to operator
symbols in the Python syntax and the functions in the
\refmodule{operator} module.


\begin{tableiii}{l|c|l}{textrm}{Operation}{Syntax}{Function}
  \lineiii{Addition}{\code{\var{a} + \var{b}}}
          {\code{add(\var{a}, \var{b})}}
  \lineiii{Concatenation}{\code{\var{seq1} + \var{seq2}}}
          {\code{concat(\var{seq1}, \var{seq2})}}
  \lineiii{Containment Test}{\code{\var{o} in \var{seq}}}
          {\code{contains(\var{seq}, \var{o})}}
  \lineiii{Division}{\code{\var{a} / \var{b}}}
          {\code{div(\var{a}, \var{b})}}
  \lineiii{Bitwise And}{\code{\var{a} \&\ \var{b}}}
          {\code{and_(\var{a}, \var{b})}}
  \lineiii{Bitwise Exclusive Or}{\code{\var{a} \^\ \var{b}}}
          {\code{xor(\var{a}, \var{b})}}
  \lineiii{Bitwise Inversion}{\code{\~{} \var{a}}}
          {\code{invert(\var{a})}}
  \lineiii{Bitwise Or}{\code{\var{a} | \var{b}}}
          {\code{or_(\var{a}, \var{b})}}
  \lineiii{Indexed Assignment}{\code{\var{o}[\var{k}] = \var{v}}}
          {\code{setitem(\var{o}, \var{k}, \var{v})}}
  \lineiii{Indexed Deletion}{\code{del \var{o}[\var{k}]}}
          {\code{delitem(\var{o}, \var{k})}}
  \lineiii{Indexing}{\code{\var{o}[\var{k}]}}
          {\code{getitem(\var{o}, \var{k})}}
  \lineiii{Left Shift}{\code{\var{a} <\code{<} \var{b}}}
          {\code{lshift(\var{a}, \var{b})}}
  \lineiii{Modulo}{\code{\var{a} \%\ \var{b}}}
          {\code{mod(\var{a}, \var{b})}}
  \lineiii{Multiplication}{\code{\var{a} * \var{b}}}
          {\code{mul(\var{a}, \var{b})}}
  \lineiii{Negation (Arithmetic)}{\code{- \var{a}}}
          {\code{neg(\var{a})}}
  \lineiii{Negation (Logical)}{\code{not \var{a}}}
          {\code{not_(\var{a})}}
  \lineiii{Right Shift}{\code{\var{a} >\code{>} \var{b}}}
          {\code{rshift(\var{a}, \var{b})}}
  \lineiii{Sequence Repitition}{\code{\var{seq} * \var{i}}}
          {\code{repeat(\var{seq}, \var{i})}}
  \lineiii{Slice Assignment}{\code{\var{seq}[\var{i}:\var{j}]} = \var{values}}
          {\code{setslice(\var{seq}, \var{i}, \var{j}, \var{values})}}
  \lineiii{Slice Deletion}{\code{del \var{seq}[\var{i}:\var{j}]}}
          {\code{delslice(\var{seq}, \var{i}, \var{j})}}
  \lineiii{Slicing}{\code{\var{seq}[\var{i}:\var{j}]}}
          {\code{getslice(\var{seq}, \var{i}, \var{j})}}
  \lineiii{String Formatting}{\code{\var{s} \%\ \var{o}}}
          {\code{mod(\var{s}, \var{o})}}
  \lineiii{Subtraction}{\code{\var{a} - \var{b}}}
          {\code{sub(\var{a}, \var{b})}}
  \lineiii{Truth Test}{\code{\var{o}}}
          {\code{truth(\var{o})}}
\end{tableiii}