Commit | Line | Data |
---|---|---|
86530b38 AT |
1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
2 | <html> | |
3 | <head> | |
4 | <link rel="STYLESHEET" href="lib.css" type='text/css' /> | |
5 | <link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" /> | |
6 | <link rel='start' href='../index.html' title='Python Documentation Index' /> | |
7 | <link rel="first" href="lib.html" title='Python Library Reference' /> | |
8 | <link rel='contents' href='contents.html' title="Contents" /> | |
9 | <link rel='index' href='genindex.html' title='Index' /> | |
10 | <link rel='last' href='about.html' title='About this document...' /> | |
11 | <link rel='help' href='about.html' title='About this document...' /> | |
12 | <link rel="next" href="module-ConfigParser.html" /> | |
13 | <link rel="prev" href="module-sets.html" /> | |
14 | <link rel="parent" href="misc.html" /> | |
15 | <link rel="next" href="itertools-functions.html" /> | |
16 | <meta name='aesop' content='information' /> | |
17 | <title>5.16 itertools -- Functions creating iterators for efficient looping</title> | |
18 | </head> | |
19 | <body> | |
20 | <DIV CLASS="navigation"> | |
21 | <div id='top-navigation-panel' xml:id='top-navigation-panel'> | |
22 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
23 | <tr> | |
24 | <td class='online-navigation'><a rel="prev" title="5.15.4 Comparison to the" | |
25 | href="comparison-to-builtin-set.html"><img src='../icons/previous.png' | |
26 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
27 | <td class='online-navigation'><a rel="parent" title="5. Miscellaneous Services" | |
28 | href="misc.html"><img src='../icons/up.png' | |
29 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
30 | <td class='online-navigation'><a rel="next" title="5.16.1 Itertool functions" | |
31 | href="itertools-functions.html"><img src='../icons/next.png' | |
32 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
33 | <td align="center" width="100%">Python Library Reference</td> | |
34 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
35 | href="contents.html"><img src='../icons/contents.png' | |
36 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
37 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' | |
38 | border='0' height='32' alt='Module Index' width='32' /></a></td> | |
39 | <td class='online-navigation'><a rel="index" title="Index" | |
40 | href="genindex.html"><img src='../icons/index.png' | |
41 | border='0' height='32' alt='Index' width='32' /></A></td> | |
42 | </tr></table> | |
43 | <div class='online-navigation'> | |
44 | <b class="navlabel">Previous:</b> | |
45 | <a class="sectref" rel="prev" href="comparison-to-builtin-set.html">5.15.4 Comparison to the</A> | |
46 | <b class="navlabel">Up:</b> | |
47 | <a class="sectref" rel="parent" href="misc.html">5. Miscellaneous Services</A> | |
48 | <b class="navlabel">Next:</b> | |
49 | <a class="sectref" rel="next" href="itertools-functions.html">5.16.1 Itertool functions</A> | |
50 | </div> | |
51 | <hr /></div> | |
52 | </DIV> | |
53 | <!--End of Navigation Panel--> | |
54 | ||
55 | <H1><A NAME="SECTION0071600000000000000000"> | |
56 | 5.16 <tt class="module">itertools</tt> -- | |
57 | Functions creating iterators for efficient looping</A> | |
58 | </H1> | |
59 | ||
60 | <P> | |
61 | <A NAME="module-itertools"></A> | |
62 | ||
63 | <span class="versionnote">New in version 2.3.</span> | |
64 | ||
65 | <P> | |
66 | This module implements a number of iterator building blocks inspired | |
67 | by constructs from the Haskell and SML programming languages. Each | |
68 | has been recast in a form suitable for Python. | |
69 | ||
70 | <P> | |
71 | The module standardizes a core set of fast, memory efficient tools | |
72 | that are useful by themselves or in combination. Standardization helps | |
73 | avoid the readability and reliability problems which arise when many | |
74 | different individuals create their own slightly varying implementations, | |
75 | each with their own quirks and naming conventions. | |
76 | ||
77 | <P> | |
78 | The tools are designed to combine readily with one another. This makes | |
79 | it easy to construct more specialized tools succinctly and efficiently | |
80 | in pure Python. | |
81 | ||
82 | <P> | |
83 | For instance, SML provides a tabulation tool: <code>tabulate(f)</code> | |
84 | which produces a sequence <code>f(0), f(1), ...</code>. This toolbox | |
85 | provides <tt class="function">imap()</tt> and <tt class="function">count()</tt> which can be combined | |
86 | to form <code>imap(f, count())</code> and produce an equivalent result. | |
87 | ||
88 | <P> | |
89 | Likewise, the functional tools are designed to work well with the | |
90 | high-speed functions provided by the <tt class="module"><a href="module-operator.html">operator</a></tt> module. | |
91 | ||
92 | <P> | |
93 | The module author welcomes suggestions for other basic building blocks | |
94 | to be added to future versions of the module. | |
95 | ||
96 | <P> | |
97 | Whether cast in pure python form or compiled code, tools that use iterators | |
98 | are more memory efficient (and faster) than their list based counterparts. | |
99 | Adopting the principles of just-in-time manufacturing, they create | |
100 | data when and where needed instead of consuming memory with the | |
101 | computer equivalent of ``inventory''. | |
102 | ||
103 | <P> | |
104 | The performance advantage of iterators becomes more acute as the number | |
105 | of elements increases - at some point, lists grow large enough to | |
106 | severely impact memory cache performance and start running slowly. | |
107 | ||
108 | <P> | |
109 | <div class="seealso"> | |
110 | <p class="heading">See Also:</p> | |
111 | ||
112 | <div class="seetext"><p>The Standard ML Basis Library, | |
113 | <em class="citetitle"><a | |
114 | href="http://www.standardml.org/Basis/" | |
115 | title="The Standard ML Basis Library" | |
116 | >The Standard ML Basis Library</a></em>.</p></div> | |
117 | ||
118 | <P> | |
119 | <div class="seetext"><p>Haskell, A Purely Functional Language, | |
120 | <em class="citetitle"><a | |
121 | href="http://www.haskell.org/definition/" | |
122 | title="Definition of Haskell and the Standard Libraries" | |
123 | >Definition of Haskell and the Standard Libraries</a></em>.</p></div> | |
124 | </div> | |
125 | ||
126 | <P> | |
127 | ||
128 | <p><br /></p><hr class='online-navigation' /> | |
129 | <div class='online-navigation'> | |
130 | <!--Table of Child-Links--> | |
131 | <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a> | |
132 | ||
133 | <UL CLASS="ChildLinks"> | |
134 | <LI><A href="itertools-functions.html">5.16.1 Itertool functions</a> | |
135 | <LI><A href="itertools-example.html">5.16.2 Examples</a> | |
136 | <LI><A href="itertools-recipes.html">5.16.3 Recipes</a> | |
137 | </ul> | |
138 | <!--End of Table of Child-Links--> | |
139 | </div> | |
140 | ||
141 | <DIV CLASS="navigation"> | |
142 | <div class='online-navigation'> | |
143 | <p></p><hr /> | |
144 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
145 | <tr> | |
146 | <td class='online-navigation'><a rel="prev" title="5.15.4 Comparison to the" | |
147 | href="comparison-to-builtin-set.html"><img src='../icons/previous.png' | |
148 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
149 | <td class='online-navigation'><a rel="parent" title="5. Miscellaneous Services" | |
150 | href="misc.html"><img src='../icons/up.png' | |
151 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
152 | <td class='online-navigation'><a rel="next" title="5.16.1 Itertool functions" | |
153 | href="itertools-functions.html"><img src='../icons/next.png' | |
154 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
155 | <td align="center" width="100%">Python Library Reference</td> | |
156 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
157 | href="contents.html"><img src='../icons/contents.png' | |
158 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
159 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' | |
160 | border='0' height='32' alt='Module Index' width='32' /></a></td> | |
161 | <td class='online-navigation'><a rel="index" title="Index" | |
162 | href="genindex.html"><img src='../icons/index.png' | |
163 | border='0' height='32' alt='Index' width='32' /></A></td> | |
164 | </tr></table> | |
165 | <div class='online-navigation'> | |
166 | <b class="navlabel">Previous:</b> | |
167 | <a class="sectref" rel="prev" href="comparison-to-builtin-set.html">5.15.4 Comparison to the</A> | |
168 | <b class="navlabel">Up:</b> | |
169 | <a class="sectref" rel="parent" href="misc.html">5. Miscellaneous Services</A> | |
170 | <b class="navlabel">Next:</b> | |
171 | <a class="sectref" rel="next" href="itertools-functions.html">5.16.1 Itertool functions</A> | |
172 | </div> | |
173 | </div> | |
174 | <hr /> | |
175 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
176 | </DIV> | |
177 | <!--End of Navigation Panel--> | |
178 | <ADDRESS> | |
179 | See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. | |
180 | </ADDRESS> | |
181 | </BODY> | |
182 | </HTML> |