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Present each feature in terms of what makes it useful or desirable.
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@ -79,8 +79,8 @@ on how the arguments compare.
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\var{key} should be a single-argument function that takes a list
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element and returns a comparison key for the element. The list is
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then sorted using the comparison keys. The following example sorts a list
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case-insensitively:
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then sorted using the comparison keys. The following example sorts a
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list case-insensitively:
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\begin{verbatim}
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>>> L = ['A', 'b', 'c', 'D']
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@ -101,31 +101,71 @@ using a \var{key} parameter. Using \var{key} results in calling the
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\method{lower()} method once for each element in the list while using
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\var{cmp} will call the method twice for each comparison.
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Note, for simple key functions and comparison functions, it is often
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possible to avoid the \keyword{lambda} expression by using an unbound
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method instead. For example, the above case-insensitive sort is best
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coded as:
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\begin{verbatim}
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>>> L.sort(key=str.lower)
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>>> L
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['A', 'b', 'c', 'D']
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\end{verbatim}
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The \var{reverse} parameter should have a Boolean value. If the value is
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\constant{True}, the list will be sorted into reverse order. Instead
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of \code{L.sort() ; L.reverse()}, you can now write
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\code{L.sort(reverse=True)}.
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of \code{L.sort(lambda x,y: cmp(y.score, x.score))}, you can now write:
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\code{L.sort(key = lambda x: x.score, reverse=True)}.
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\item The list type gained a \method{sorted(iterable)} method that
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returns the elements of the iterable as a sorted list. It also accepts
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the \var{cmp}, \var{key}, and \var{reverse} keyword arguments, same as
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the \method{sort()} method. An example usage:
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The results of sorting are now guaranteed to be stable. This means that
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two entries with equal keys will be returned in the same order as
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they were input.
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\item The list type gained a \method{sorted(iterable)} method that works
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like the in-place \method{sort()} method but has been made suitable for
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use in expressions. The differences are:
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\begin{itemize}
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\item the input make be any iterable;
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\item a copy is sorted, leaving the original intact; and
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\item the expression returns the new sorted copy
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\end{itemize}
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\begin{verbatim}
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>>> L = [9,7,8,3,2,4,1,6,5]
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>>> list.sorted(L)
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[1, 2, 3, 4, 5, 6, 7, 8, 9]
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>>> L
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[9, 7, 8, 3, 2, 4, 1, 6, 5]
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>>>
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>>> [10+i for i in list.sorted(L)] # usable in a list comprehension
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[11, 12, 13, 14, 15, 16, 17, 18, 19]
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>>> L = [9,7,8,3,2,4,1,6,5] # original is left unchanged
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[9,7,8,3,2,4,1,6,5]
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>>> list.sorted('Monte Python') # any iterable may be an input
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[' ', 'M', 'P', 'e', 'h', 'n', 'n', 'o', 'o', 't', 't', 'y']
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>>> colormap = dict(red=1, blue=2, green=3, black=4, yellow=5)
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>>> for k, v in list.sorted(colormap.iteritems()):
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... print k, v
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...
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black 4
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blue 2
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green 3
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red 1
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yellow 5
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\end{verbatim}
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Note that the original list is unchanged; the list returned by
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\method{sorted()} is a newly-created one.
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\item The \function{zip()} built-in function and \function{itertools.izip()} now return an empty list
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instead of raising a \exception{TypeError} exception if called
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with no arguments.
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\item The \function{zip()} built-in function and \function{itertools.izip()}
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now return an empty list instead of raising a \exception{TypeError}
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exception if called with no arguments. This makes the functions more
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suitable for use with variable length argument lists:
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\begin{verbatim}
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>>> def transpose(array):
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... return zip(*array)
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...
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>>> transpose([(1,2,3), (4,5,6)])
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[(1, 4), (2, 5), (3, 6)]
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>>> transpose([])
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[]
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\end{verbatim}
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\end{itemize}
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@ -161,11 +201,15 @@ details.
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supports transparency, this makes it possible to use a transparent background.
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(Contributed by J\"org Lehmann.)
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\item The \module{heapq} module is no longer implemented in Python,
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having been converted into C.
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\item The \module{heapq} module has been converted to C. The resulting
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ten-fold improvement in speed makes the module suitable for handling
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high volumes of data.
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\item The \module{random} module has a new method called \method{getrandbits(N)}
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which returns an N-bit long integer.
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which returns an N-bit long integer. This method supports the existing
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\method{randrange()} method, making it possible to efficiently generate
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arbitrarily large random numbers (suitable for prime number generation in
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RSA applications).
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\item The regular expression language accepted by the \module{re} module
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was extended with simple conditional expressions, written as
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@ -231,9 +275,9 @@ changes to your code:
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\begin{itemize}
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\item The \function{zip()} built-in function and \function{itertools.izip()} now return an empty list
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instead of raising a \exception{TypeError} exception if called
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with no arguments.
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\item The \function{zip()} built-in function and \function{itertools.izip()}
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now return an empty list instead of raising a \exception{TypeError}
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exception if called with no arguments.
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\item \function{dircache.listdir()} now passes exceptions to the caller
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instead of returning empty lists.
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