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Diffstat (limited to 'Doc')
| -rw-r--r-- | Doc/whatsnew/whatsnew24.tex | 37 |
1 files changed, 15 insertions, 22 deletions
diff --git a/Doc/whatsnew/whatsnew24.tex b/Doc/whatsnew/whatsnew24.tex index b25caea..f5890a1 100644 --- a/Doc/whatsnew/whatsnew24.tex +++ b/Doc/whatsnew/whatsnew24.tex @@ -14,8 +14,8 @@ \maketitle \tableofcontents -This article explains the new features in Python 2.4. No release date -for Python 2.4 has been set; expect that this will happen mid-2004. +This article explains the new features in Python 2.4. The release +date is expected to be around September 2004. While Python 2.3 was primarily a library development release, Python 2.4 may extend the core language and interpreter in @@ -91,12 +91,12 @@ XXX write this. %====================================================================== \section{PEP 229: Generator Expressions} -Generator expressions create in-line generators using a syntax similar -to list comprehensions but with parenthesis instead of the surrounding -brackets. - -Genexps allow simple generators to be constructed without a separate function -definition. Writing: +Now, simple generators can be coded succinctly as expressions using a syntax +like list comprehensions but with parentheses instead of brackets. These +expressions are designed for situations where the generator is used right +away by an enclosing function. Generator expressions are more compact but +less versatile than full generator definitions and the tend to be more memory +friendly than equivalent list comprehensions. \begin{verbatim} g = (tgtexp for var1 in exp1 for var2 in exp2 if exp3) @@ -121,11 +121,9 @@ a whole list is memory all at once. Applications using memory friendly generator expressions may scale-up to high volumes of data more readily than with list comprehensions. -Generator expressions are intended to be used inside functions -such as \function{sum()}, \function{min()}, \function{set()}, and -\function{dict()}. These functions consume their data all at once -and would not benefit from having a full list instead of a generator -as an input: +Generator expressions are best used in functions that consume their +data all at once and would not benefit from having a full list instead +of a generator as an input: \begin{verbatim} >>> sum(i*i for i in range(10)) @@ -149,20 +147,15 @@ as an input: \end{verbatim} -These examples show the intended use for generator expressions -in situations where the values get consumed immediately after the -generator is created. In these situations, they operate like -memory efficient versions of list comprehensions. - For more complex uses of generators, it is strongly recommended that the traditional full generator definitions be used instead. In a generator expression, the first for-loop expression is evaluated as soon as the expression is defined while the other expressions do not get evaluated until the generator is run. This nuance is never -an issue when the generator is used immediately. If it is not used -right away, then it is better to write a full generator definition -which more clearly reveals when the expressions are evaluated and is -more obvious about the visibility and lifetime of its looping variables. +an issue when the generator is used immediately; however, if it is not +used right away, a full generator definition would be much more clear +about when the sub-expressions are evaluated and would be more obvious +about the visibility and lifetime of the variables. \begin{seealso} \seepep{289}{Generator Expressions}{Proposed by Raymond Hettinger and |