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| -rw-r--r-- | Doc/ref/ref5.tex | 37 |
1 files changed, 7 insertions, 30 deletions
diff --git a/Doc/ref/ref5.tex b/Doc/ref/ref5.tex index 8fae716..1930b29 100644 --- a/Doc/ref/ref5.tex +++ b/Doc/ref/ref5.tex @@ -955,11 +955,16 @@ invent a value anyway, it does not bother to return a value of the same type as its argument, so e.g., \code{not 'foo'} yields \code{0}, not \code{''}.) +\section{Lambdas\label{lambdas}} +\indexii{lambda}{expression} +\indexii{lambda}{form} +\indexii{anonmymous}{function} + Lambda forms (lambda expressions) have the same syntactic position as expressions. They are a shorthand to create anonymous functions; the expression \code{lambda \var{arguments}: \var{expression}} -yields a function object that behaves virtually identical to one -defined with +yields a function object. The unnamed object behaves like a function +object define with \begin{verbatim} def name(arguments): @@ -969,34 +974,6 @@ def name(arguments): See section \ref{function} for the syntax of parameter lists. Note that functions created with lambda forms cannot contain statements. \label{lambda} -\indexii{lambda}{expression} -\indexii{lambda}{form} -\indexii{anonmymous}{function} - -\strong{Programmer's note:} Prior to Python 2.1, a lambda form defined -inside a function has no access to names defined in the function's -namespace. This is because Python had only two scopes: local and -global. A common work-around was to use default argument values to -pass selected variables into the lambda's namespace, e.g.: - -\begin{verbatim} -def make_incrementor(increment): - return lambda x, n=increment: x+n -\end{verbatim} - -As of Python 2.1, nested scopes were introduced, and this work-around -has not been necessary. Python 2.1 supports nested scopes in modules -which include the statement \samp{from __future__ import -nested_scopes}, and more recent versions of Python enable nested -scopes by default. This version works starting with Python 2.1: - -\begin{verbatim} -from __future__ import nested_scopes - -def make_incrementor(increment): - return lambda x: x+increment -\end{verbatim} - \section{Expression lists\label{exprlists}} \indexii{expression}{list} |