Python中的集合set

>>> help(set)
Help on class set in module __builtin__:

class set(object)
 |  set(iterable) --> set object
 |
 |  Build an unordered collection of unique elements.#无序、独一无二的元素
 |
 |  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 x.__class__.__doc__ 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 sets as a new set.
 |
 |      (i.e. all elements that are in both 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 at 0x1E1CD668>
 |      T.__new__(S, ...) -> a new object with type S, a subtype of T

通过下面例子，可以看出：集合是非重复的，集合是无序的。

>>> d=set('chooses')
>>> d
set(['h', 'c', 'e', 's', 'o'])
>>> d
set(['h', 'c', 'e', 's', 'o'])
>>> d
set(['h', 'c', 'e', 's', 'o'])
>>>

如果需要有序的集合，可以改为list：

>>> d=set('chooses')
>>> d
set(['h', 'c', 'e', 's', 'o'])
>>> d
set(['h', 'c', 'e', 's', 'o'])
>>> d
set(['h', 'c', 'e', 's', 'o'])
>>> mylist=list(d)
>>> mylist
['h', 'c', 'e', 's', 'o']
>>> mylist.sort()
>>> mylist
['c', 'e', 'h', 'o', 's']
>>>