Present each feature in terms of what makes it useful or desirable.

This commit is contained in:
Raymond Hettinger 2003-11-12 16:27:50 +00:00
parent 859db26729
commit 607c00f792
1 changed files with 68 additions and 24 deletions

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