File: //usr/share/doc/python-docs-2.4.3/html/lib/itertools-recipes.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<link rel="STYLESHEET" href="lib.css" type='text/css' />
<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
<link rel='start' href='../index.html' title='Python Documentation Index' />
<link rel="first" href="lib.html" title='Python Library Reference' />
<link rel='contents' href='contents.html' title="Contents" />
<link rel='index' href='genindex.html' title='Index' />
<link rel='last' href='about.html' title='About this document...' />
<link rel='help' href='about.html' title='About this document...' />
<link rel="prev" href="itertools-example.html" />
<link rel="parent" href="module-itertools.html" />
<link rel="next" href="module-ConfigParser.html" />
<meta name='aesop' content='information' />
<title>5.16.3 Recipes </title>
</head>
<body>
<DIV CLASS="navigation">
<div id='top-navigation-panel' xml:id='top-navigation-panel'>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="5.16.2 Examples"
href="itertools-example.html"><img src='../icons/previous.png'
border='0' height='32' alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="5.16 itertools "
href="module-itertools.html"><img src='../icons/up.png'
border='0' height='32' alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="5.17 ConfigParser "
href="module-ConfigParser.html"><img src='../icons/next.png'
border='0' height='32' alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
href="contents.html"><img src='../icons/contents.png'
border='0' height='32' alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
border='0' height='32' alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
href="genindex.html"><img src='../icons/index.png'
border='0' height='32' alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="itertools-example.html">5.16.2 Examples</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="module-itertools.html">5.16 itertools </A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="module-ConfigParser.html">5.17 ConfigParser </A>
</div>
<hr /></div>
</DIV>
<!--End of Navigation Panel-->
<H2><A NAME="SECTION0071630000000000000000"></A><A NAME="itertools-recipes"></A>
<BR>
5.16.3 Recipes
</H2>
<P>
This section shows recipes for creating an extended toolset using the
existing itertools as building blocks.
<P>
The extended tools offer the same high performance as the underlying
toolset. The superior memory performance is kept by processing elements one
at a time rather than bringing the whole iterable into memory all at once.
Code volume is kept small by linking the tools together in a functional style
which helps eliminate temporary variables. High speed is retained by
preferring ``vectorized'' building blocks over the use of for-loops and
generators which incur interpreter overhead.
<P>
<div class="verbatim"><pre>
def take(n, seq):
return list(islice(seq, n))
def enumerate(iterable):
return izip(count(), iterable)
def tabulate(function):
"Return function(0), function(1), ..."
return imap(function, count())
def iteritems(mapping):
return izip(mapping.iterkeys(), mapping.itervalues())
def nth(iterable, n):
"Returns the nth item"
return list(islice(iterable, n, n+1))
def all(seq, pred=bool):
"Returns True if pred(x) is True for every element in the iterable"
for elem in ifilterfalse(pred, seq):
return False
return True
def any(seq, pred=bool):
"Returns True if pred(x) is True for at least one element in the iterable"
for elem in ifilter(pred, seq):
return True
return False
def no(seq, pred=bool):
"Returns True if pred(x) is False for every element in the iterable"
for elem in ifilter(pred, seq):
return False
return True
def quantify(seq, pred=bool):
"Count how many times the predicate is True in the sequence"
return sum(imap(pred, seq))
def padnone(seq):
"""Returns the sequence elements and then returns None indefinitely.
Useful for emulating the behavior of the built-in map() function.
"""
return chain(seq, repeat(None))
def ncycles(seq, n):
"Returns the sequence elements n times"
return chain(*repeat(seq, n))
def dotproduct(vec1, vec2):
return sum(imap(operator.mul, vec1, vec2))
def flatten(listOfLists):
return list(chain(*listOfLists))
def repeatfunc(func, times=None, *args):
"""Repeat calls to func with specified arguments.
Example: repeatfunc(random.random)
"""
if times is None:
return starmap(func, repeat(args))
else:
return starmap(func, repeat(args, times))
def pairwise(iterable):
"s -> (s0,s1), (s1,s2), (s2, s3), ..."
a, b = tee(iterable)
try:
b.next()
except StopIteration:
pass
return izip(a, b)
def grouper(n, iterable, padvalue=None):
"grouper(3, 'abcdefg', 'x') --> ('a','b','c'), ('d','e','f'), ('g','x','x')"
return izip(*[chain(iterable, repeat(padvalue, n-1))]*n)
</pre></div>
<DIV CLASS="navigation">
<div class='online-navigation'>
<p></p><hr />
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="5.16.2 Examples"
href="itertools-example.html"><img src='../icons/previous.png'
border='0' height='32' alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="5.16 itertools "
href="module-itertools.html"><img src='../icons/up.png'
border='0' height='32' alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="5.17 ConfigParser "
href="module-ConfigParser.html"><img src='../icons/next.png'
border='0' height='32' alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
href="contents.html"><img src='../icons/contents.png'
border='0' height='32' alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
border='0' height='32' alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
href="genindex.html"><img src='../icons/index.png'
border='0' height='32' alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="itertools-example.html">5.16.2 Examples</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="module-itertools.html">5.16 itertools </A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="module-ConfigParser.html">5.17 ConfigParser </A>
</div>
</div>
<hr />
<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
</DIV>
<!--End of Navigation Panel-->
<ADDRESS>
See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
</ADDRESS>
</BODY>
</HTML>