python 系统学习笔记（七）---set

1. 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sysmmetricdifference(对称差集)等数学运算.
2. sets支持xinset,len(set),和forxinset。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.

|

| Methods defined here:

|

| __and__(...)

| x.__and__(y) <==> x&y

|

| __cmp__(...)

| x.__cmp__(y) <==> cmp(x,y)

|

| __contains__(...)

| x.__contains__(y) <==> y in x.

|

| __eq__(...)

| x.__eq__(y) <==> x==y

|

| __ge__(...)

| x.__ge__(y) <==> x>=y

|

| __getattribute__(...)

| x.__getattribute__('name') <==> x.name

|

| __gt__(...)

| x.__gt__(y) <==> x>y

|

| __iand__(...)

| x.__iand__(y) <==> x&y

|

| __init__(...)

| x.__init__(...) initializes x; see help(type(x)) for signature

|

| __ior__(...)

| x.__ior__(y) <==> x|y

|

| __isub__(...)

| x.__isub__(y) <==> x-y

|

| __iter__(...)

| x.__iter__() <==> iter(x)

|

| __ixor__(...)

| x.__ixor__(y) <==> x^y

|

| __le__(...)

| x.__le__(y) <==> x<=y

|

| __len__(...)

| x.__len__() <==> len(x)

|

| __lt__(...)

| x.__lt__(y) <==> x<y

|

| __ne__(...)

| x.__ne__(y) <==> x!=y

|

| __or__(...)

| x.__or__(y) <==> x|y

|

| __rand__(...)

| x.__rand__(y) <==> y&x

|

| __reduce__(...)

| Return state information for pickling.

|

| __repr__(...)

| x.__repr__() <==> repr(x)

|

| __ror__(...)

| x.__ror__(y) <==> y|x

|

| __rsub__(...)

| x.__rsub__(y) <==> y-x

|

| __rxor__(...)

| x.__rxor__(y) <==> y^x

|

| __sizeof__(...)

| S.__sizeof__() -> size of S in memory, in bytes

|

| __sub__(...)

| x.__sub__(y) <==> x-y

|

| __xor__(...)

| x.__xor__(y) <==> x^y

|

| add(...)

| Add an element to a set.

|

| This has no effect if the element is already present.

|

| clear(...)

| Remove all elements from this set.

|

| copy(...)

| Return a shallow copy of a set.

|

| difference(...)

| Return the difference of two or more sets as a new set.

|

| (i.e. all elements that are in this set but not the others.)

|

| difference_update(...)

| Remove all elements of another set from this set.

|

| discard(...)

| Remove an element from a set if it is a member.

|

| If the element is not a member, do nothing.

|

| intersection(...)

| Return the intersection of two or more sets as a new set.

|

| (i.e. elements that are common to all of the sets.)

|

| intersection_update(...)

| Update a set with the intersection of itself and another.

|

| isdisjoint(...)

| Return True if two sets have a null intersection.

|

| issubset(...)

| Report whether another set contains this set.

|

| issuperset(...)

| Report whether this set contains another set.

|

| pop(...)

| Remove and return an arbitrary set element.

| Raises KeyError if the set is empty.

|

| remove(...)

| Remove an element from a set; it must be a member.

|

| If the element is not a member, raise a KeyError.

|

| symmetric_difference(...)

| Return the symmetric difference of two sets as a new set.

|

| (i.e. all elements that are in exactly one of the sets.)

|

| symmetric_difference_update(...)

| Update a set with the symmetric difference of itself and another.

|

| union(...)

| Return the union of sets as a new set.

|

| (i.e. all elements that are in either set.)

|

| update(...)

| Update a set with the union of itself and others.

|

| ----------------------------------------------------------------------

| Data and other attributes defined here:

|

| __hash__ = None

|

| __new__ = <built-in method __new__ of type object>

| 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

1. 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（operatorbasedcounterparts）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。
2. 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）
3. 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<b,a==b,或者a>b。因此，sets不提供__cmp__方法。
4. 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。