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']
 >>>