python 系统学习笔记（七）---set
- python的set和其他语言类似, 是一个无序不重复元素集, 基本功能包括关系测试和消除重复元素. 集合对象还支持union(联合), intersection(交), difference(差)和sysmmetric difference(对称差集)等数学运算.
- sets 支持 x in set, len(set),和 for x in set。作为一个无序的集合，sets不记录元素位置或者插入点。因此，sets不支持 indexing, slicing, 或其它类序列（sequence-like）的操作。
Help on class set in module __builtin__:
class set(object)
| set() -> new empty set object
| set(iterable) -> new set object
|
| Build an unordered collection of unique elements.
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| Methods defined here:
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| __and__(...)
| x.__and__(y) <==> x&y
|
| __cmp__(...)
| x.__cmp__(y) <==> cmp(x,y)
|
| __contains__(...)
| x.__contains__(y) <==> y in x.
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| __eq__(...)
| x.__eq__(y) <==> x==y
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| __ge__(...)
| x.__ge__(y) <==> x>=y
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| __getattribute__(...)
| x.__getattribute__('name') <==> x.name
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| __gt__(...)
| x.__gt__(y) <==> x>y
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| __iand__(...)
| x.__iand__(y) <==> x&y
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| __init__(...)
| x.__init__(...) initializes x; see help(type(x)) for signature
|
| __ior__(...)
| x.__ior__(y) <==> x|y
|
| __isub__(...)
| x.__isub__(y) <==> x-y
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| __iter__(...)
| x.__iter__() <==> iter(x)
|
| __ixor__(...)
| x.__ixor__(y) <==> x^y
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| __le__(...)
| x.__le__(y) <==> x<=y
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| __len__(...)
| x.__len__() <==> len(x)
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| __lt__(...)
| x.__lt__(y) <==> x
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| __ne__(...)
| x.__ne__(y) <==> x!=y
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| __or__(...)
| x.__or__(y) <==> x|y
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| __rand__(...)
| x.__rand__(y) <==> y&x
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| __reduce__(...)
| Return state information for pickling.
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| __repr__(...)
| x.__repr__() <==> repr(x)
|
| __ror__(...)
| x.__ror__(y) <==> y|x
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| __rsub__(...)
| x.__rsub__(y) <==> y-x
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| __rxor__(...)
| x.__rxor__(y) <==> y^x
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| __sizeof__(...)
| S.__sizeof__() -> size of S in memory, in bytes
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| __sub__(...)
| x.__sub__(y) <==> x-y
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| __xor__(...)
| x.__xor__(y) <==> x^y
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| add(...)
| Add an element to a set.
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| This has no effect if the element is already present.
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| clear(...)
| Remove all elements from this set.
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| copy(...)
| Return a shallow copy of a set.
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| difference(...)
| Return the difference of two or more sets as a new set.
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| (i.e. all elements that are in this set but not the others.)
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| difference_update(...)
| Remove all elements of another set from this set.
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| discard(...)
| Remove an element from a set if it is a member.
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| If the element is not a member, do nothing.
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| intersection(...)
| Return the intersection of two or more sets as a new set.
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| (i.e. elements that are common to all of the sets.)
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| intersection_update(...)
| Update a set with the intersection of itself and another.
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| isdisjoint(...)
| Return True if two sets have a null intersection.
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| issubset(...)
| Report whether another set contains this set.
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| issuperset(...)
| Report whether this set contains another set.
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| pop(...)
| Remove and return an arbitrary set element.
| Raises KeyError if the set is empty.
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| remove(...)
| Remove an element from a set; it must be a member.
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| If the element is not a member, raise a KeyError.
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| symmetric_difference(...)
| Return the symmetric difference of two sets as a new set.
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| (i.e. all elements that are in exactly one of the sets.)
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| symmetric_difference_update(...)
| Update a set with the symmetric difference of itself and another.
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| union(...)
| Return the union of sets as a new set.
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| (i.e. all elements that are in either set.)
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| update(...)
| Update a set with the union of itself and others.
|
| ----------------------------------------------------------------------
| Data and other attributes defined here:
|
| __hash__ = None
|
| __new__ =
| T.__new__(S, ...) -> a new object with type S, a subtype of T
# -*- coding: cp936 -*-
print help(set)
#set(['h', 'e', 'l', 'o'])
x=set('hello')
print x
#set(['d', 'r', 'o', 'w', 'l'])
y=set('world')
print y
# 交集
print x&y
#set(['l', 'o'])
print x|y # 并集
#set(['e', 'd', 'h', 'l', 'o', 'r', 'w'])
print x - y # 差集
#set(['h', 'e'])
print x^y # 对称差集（项在t或s中，但不会同时出现在二者中）
a = [11,22,33,44,11,22]
print set(a)
#set([33, 11, 44, 22])
print [i for i in set(a)] #去重
s=set('hello')
t=set('world')
len(s)
#set 的长度
x='h'
print x in s
#测试 x 是否是 s 的成员
x not in s
#测试 x 是否不是 s 的成员
s.issubset(t)
#s <= t
#测试是否 s 中的每一个元素都在 t 中
s.issuperset(t)
s >= t
#测试是否 t 中的每一个元素都在 s 中
s.union(t)
s | t
#返回一个新的 set 包含 s 和 t 中的每一个元素
s.intersection(t)
s & t
#返回一个新的 set 包含 s 和 t 中的公共元素
s.difference(t)
s - t
#返回一个新的 set 包含 s 中有但是 t 中没有的元素
s.symmetric_difference(t)
s ^ t
#返回一个新的 set 包含 s 和 t 中不重复的元素
s.copy()
#回 set “s”的一个浅复制
- 请注意：union(), intersection(), difference() 和 symmetric_difference() 的非运算符（non-operator，就是形如 s.union()这样的）版本将会接受任何 iterable 作为参数。相反，它们的运算符版本（operator based counterparts）要求参数必须是 sets。这样可以避免潜在的错误，如：为了更可读而使用 set('abc') & 'cbs' 来替代 set('abc').intersection('cbs')。从 2.3.1 版本中做的更改：以前所有参数都必须是 sets。
- 另外，Set 和 ImmutableSet 两者都支持 set 与 set 之间的比较。两个 sets 在也只有在这种情况下是相等的：每一个 set 中的元素都是另一个中的元素（二者互为subset）。一个 set 比另一个 set 小，只有在第一个 set 是第二个 set 的 subset 时（是一个 subset，但是并不相等）。一个 set 比另一个 set 打，只有在第一个 set 是第二个 set 的 superset 时（是一个 superset，但是并不相等）
- 子 set 和相等比较并不产生完整的排序功能。例如：任意两个 sets 都不相等也不互为子 set，因此以下的运算都会返回 False：a
- 因为 sets 只定义了部分排序功能（subset 关系），list.sort() 方法的输出对于 sets 的列表没有定义。