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