diff options
| -rw-r--r-- | Doc/whatsnew/whatsnew23.tex | 101 |
1 files changed, 85 insertions, 16 deletions
diff --git a/Doc/whatsnew/whatsnew23.tex b/Doc/whatsnew/whatsnew23.tex index ada6f07..85a7972 100644 --- a/Doc/whatsnew/whatsnew23.tex +++ b/Doc/whatsnew/whatsnew23.tex @@ -833,6 +833,16 @@ creates a dictionary with keys taken from the supplied iterator (Patches contributed by Raymond Hettinger.) +The dict() constructor now also accepts keyword arguments to simplify +creating small dictionaries: + +\begin{verbatim} +>>> dict(red=1, blue=2, green=3, black=4) +{'blue': 2, 'black': 4, 'green': 3, 'red': 1} +\end{verbatim} + +(Contributed by Just van Rossum.) + \item The \keyword{assert} statement no longer checks the \code{__debug__} flag, so you can no longer disable assertions by assigning to \code{__debug__}. Running Python with the \programopt{-O} switch will still generate @@ -1014,6 +1024,10 @@ and significantly reworked by Tim Peters.) small speed increase, subject to your compiler's idiosyncrasies. (Removed by Michael Hudson.) +\item \function{xrange()} objects now have their own iterator, making +\code{for i in xrange(n)} slightly faster than +\code{for i in range(n)}. (Patch by Raymond Hettinger.) + \item A number of small rearrangements have been made in various hotspots to improve performance, inlining a function here, removing some code there. (Implemented mostly by GvR, but lots of people have @@ -1177,28 +1191,30 @@ will enable buffering. \item The \function{sample(\var{population}, \var{k})} function was added to the \module{random} module. \var{population} is a sequence -containing the elements of a population, and \function{sample()} +or \code{xrange} object containing the elements of a population, and \function{sample()} chooses \var{k} elements from the population without replacing chosen elements. \var{k} can be any value up to \code{len(\var{population})}. For example: \begin{verbatim} ->>> pop = range(6) ; pop -[0, 1, 2, 3, 4, 5] ->>> random.sample(pop, 3) # Choose three elements -[0, 4, 3] ->>> random.sample(pop, 6) # Choose all six elements -[4, 5, 0, 3, 2, 1] ->>> random.sample(pop, 6) # Choose six again -[4, 2, 3, 0, 5, 1] ->>> random.sample(pop, 7) # Can't choose more than six +>>> days = ['Mo', 'Tu', 'We', 'Th', 'Fr', 'St', 'Sn'] +>>> random.sample(days, 3) # Choose 3 elements +['St', 'Sn', 'Th'] +>>> random.sample(days, 7) # Choose 7 elements +['Tu', 'Th', 'Mo', 'We', 'St', 'Fr', 'Sn'] +>>> random.sample(days, 7) # Choose 7 again +['We', 'Mo', 'Sn', 'Fr', 'Tu', 'St', 'Th'] +>>> random.sample(days, 8) # Can't choose eight Traceback (most recent call last): File "<stdin>", line 1, in ? - File "random.py", line 396, in sample - raise ValueError, "sample larger than population" + File "random.py", line 414, in sample + raise ValueError, "sample larger than population" ValueError: sample larger than population ->>> +>>> random.sample(xrange(1,10000,2), 10) # Choose ten odds under 10000 +[3407, 3805, 1505, 7023, 2401, 2267, 9733, 3151, 8083, 9195] \end{verbatim} + +(Contributed by Raymond Hettinger.) \item The \module{readline} module also gained a number of new functions: \function{get_history_item()}, @@ -1270,6 +1286,58 @@ sometimes have odd bugs. Brett Cannon contributed a portable implementation that's written in pure Python, which should behave identically on all platforms. +\item The \module{UserDict) has a new \class{DictMixin} class which +defines all dictionary methods for classes that already have a minimum +mapping interface. This greatly simplifies writing classes that need +to be substitutable for dictionaries, such as the classes in +the \module{shelve} module. + +Adding the mixin as a superclass provides the full dictionary +interface whenever the class defines \method{__getitem__}, +\method{__setitem__}, \method{__delitem__), and \method{keys}. +For example: + +\begin{verbatim} +>>> import UserDict +>>> class SeqDict(UserDict.DictMixin): + """Dictionary lookalike implemented with lists.""" + def __init__(self): + self.keylist = [] + self.valuelist = [] + def __getitem__(self, key): + try: + i = self.keylist.index(key) + except ValueError: + raise KeyError + return self.valuelist[i] + def __setitem__(self, key, value): + try: + i = self.keylist.index(key) + self.valuelist[i] = value + except ValueError: + self.keylist.append(key) + self.valuelist.append(value) + def __delitem__(self, key): + try: + i = self.keylist.index(key) + except ValueError: + raise KeyError + self.keylist.pop(i) + self.valuelist.pop(i) + def keys(self): + return list(self.keylist) + +>>> s = SeqDict() +>>> dir(s) # See that other dictionary methods are implemented +['__cmp__', '__contains__', '__delitem__', '__doc__', '__getitem__', + '__init__', '__iter__', '__len__', '__module__', '__repr__', + '__setitem__', 'clear', 'get', 'has_key', 'items', 'iteritems', + 'iterkeys', 'itervalues', 'keylist', 'keys', 'pop', 'popitem', + 'setdefault', 'update', 'valuelist', 'values'] +\end {verbatim} + +(Contributed by Raymond Hettinger.) + \item The DOM implementation in \module{xml.dom.minidom} can now generate XML output in a particular encoding, by specifying an optional encoding argument to @@ -1711,8 +1779,9 @@ name. The author would like to thank the following people for offering suggestions, corrections and assistance with various drafts of this article: Simon Brunning, Michael Chermside, Scott David Daniels, -Fred~L. Drake, Jr., Michael Hudson, Detlef Lannert, Martin von -L\"owis, Andrew MacIntyre, Lalo Martins, Gustavo Niemeyer, Neal -Norwitz, Chris Reedy, Vinay Sajip, Neil Schemenauer, Jason Tishler. +Fred~L. Drake, Jr., Raymond Hettinger, Michael Hudson, Detlef Lannert, +Martin von L\"owis, Andrew MacIntyre, Lalo Martins, Gustavo Niemeyer, +Neal Norwitz, Chris Reedy, Vinay Sajip, Neil Schemenauer, Jason +Tishler. \end{document} |