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Diffstat (limited to 'Doc')
| -rw-r--r-- | Doc/whatsnew/whatsnew25.tex | 36 |
1 files changed, 29 insertions, 7 deletions
diff --git a/Doc/whatsnew/whatsnew25.tex b/Doc/whatsnew/whatsnew25.tex index b418a97..28b07a5 100644 --- a/Doc/whatsnew/whatsnew25.tex +++ b/Doc/whatsnew/whatsnew25.tex @@ -28,18 +28,40 @@ rationale, refer to the PEP for a particular new feature. %====================================================================== \section{PEP 309: Partial Function Application} -For programs written in a functional style, it can be useful to -construct variants of existing functions that have some of the -parameters filled in. This is called ``partial function application''. -The new \module{functional} module contains a \class{partial} class -that provides partial application. - The \module{functional} module is intended to contain tools for functional-style programming. Currently it only contains \class{partial}, but new functions will probably be added in future versions of Python. -% XXX write rest of this +For programs written in a functional style, it can be useful to +construct variants of existing functions that have some of the +parameters filled in. Consider a Python function \code{f(a, b, c)}; +you could create a new function \code{g(b, c)} that was equivalent to +\code{f(1, b, c)}. This is called ``partial function application'', +and is provided by the \class{partial} class in the new +\module{functional} module. + +The constructor for \class{partial} takes the arguments +\code{(\var{function}, \var{arg1}, \var{arg2}, ... +\var{kwarg1}=\var{value1}, \var{kwarg2}=\var{value2})}. The resulting +object is callable, so you can just call it to invoke \var{function} +with the filled-in arguments. + +Here's a small but realistic example: + +\begin{verbatim} +import functional + +def log (message, subsystem): + "Write the contents of 'message' to the specified subsystem." + print '%s: %s' % (subsystem, message) + ... + +server_log = functional.partial(log, subsystem='server') +\end{verbatim} + +Here's another example, from a program that uses PyGTk. + % XXX add example from my GTk programming |