projects / OpenSPARC-T2-SAM / blame
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| 53 | <H1><A NAME="SECTION000200000000000000000"> | |
| 54 | 1 PEP 218: Built-In Set Objects</A> | |
| 55 | </H1> | |
| 56 | ||
| 57 | <P> | |
| 58 | Python 2.3 introduced the <tt class="module">sets</tt> module. C implementations of | |
| 59 | set data types have now been added to the Python core as two new | |
| 60 | built-in types, <tt class="function">set(<var>iterable</var>)</tt> and | |
| 61 | <tt class="function">frozenset(<var>iterable</var>)</tt>. They provide high speed | |
| 62 | operations for membership testing, for eliminating duplicates from | |
| 63 | sequences, and for mathematical operations like unions, intersections, | |
| 64 | differences, and symmetric differences. | |
| 65 | ||
| 66 | <P> | |
| 67 | <div class="verbatim"><pre> | |
| 68 | >>> a = set('abracadabra') # form a set from a string | |
| 69 | >>> 'z' in a # fast membership testing | |
| 70 | False | |
| 71 | >>> a # unique letters in a | |
| 72 | set(['a', 'r', 'b', 'c', 'd']) | |
| 73 | >>> ''.join(a) # convert back into a string | |
| 74 | 'arbcd' | |
| 75 | ||
| 76 | >>> b = set('alacazam') # form a second set | |
| 77 | >>> a - b # letters in a but not in b | |
| 78 | set(['r', 'd', 'b']) | |
| 79 | >>> a | b # letters in either a or b | |
| 80 | set(['a', 'c', 'r', 'd', 'b', 'm', 'z', 'l']) | |
| 81 | >>> a & b # letters in both a and b | |
| 82 | set(['a', 'c']) | |
| 83 | >>> a ^ b # letters in a or b but not both | |
| 84 | set(['r', 'd', 'b', 'm', 'z', 'l']) | |
| 85 | ||
| 86 | >>> a.add('z') # add a new element | |
| 87 | >>> a.update('wxy') # add multiple new elements | |
| 88 | >>> a | |
| 89 | set(['a', 'c', 'b', 'd', 'r', 'w', 'y', 'x', 'z']) | |
| 90 | >>> a.remove('x') # take one element out | |
| 91 | >>> a | |
| 92 | set(['a', 'c', 'b', 'd', 'r', 'w', 'y', 'z']) | |
| 93 | </pre></div> | |
| 94 | ||
| 95 | <P> | |
| 96 | The <tt class="function">frozenset</tt> type is an immutable version of <tt class="function">set</tt>. | |
| 97 | Since it is immutable and hashable, it may be used as a dictionary key or | |
| 98 | as a member of another set. | |
| 99 | ||
| 100 | <P> | |
| 101 | The <tt class="module">sets</tt> module remains in the standard library, and may be | |
| 102 | useful if you wish to subclass the <tt class="class">Set</tt> or <tt class="class">ImmutableSet</tt> | |
| 103 | classes. There are currently no plans to deprecate the module. | |
| 104 | ||
| 105 | <P> | |
| 106 | <div class="seealso"> | |
| 107 | <p class="heading">See Also:</p> | |
| 108 | ||
| 109 | <dl compact="compact" class="seerfc"> | |
| 110 | <dt><a href="http://www.python.org/peps/pep-0218.html" | |
| 111 | title="Adding a Built-In Set Object Type" | |
| 112 | >PEP 218, <em>Adding a Built-In Set Object Type</em></a> | |
| 113 | <dd>Originally proposed by | |
| 114 | Greg Wilson and ultimately implemented by Raymond Hettinger. | |
| 115 | </dl> | |
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