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Kirill Smelkov
cpython
Commits
2225add2
Commit
2225add2
authored
Apr 01, 2002
by
Jeremy Hylton
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Given lambda its own section, instead of burying it in boolean operators.
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Doc/ref/ref5.tex
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2225add2
...
...
@@ -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
}
...
...
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