python3【基础】-集合

集合( set)：把不同的元素组成一起形成集合，是python基本的数据类型。

集合元素(set elements)：组成集合的成员(不可重复)

class set(object)

 |  set() -> new empty set object

 |  set(iterable) -> new set object

 |

 |  Build an unordered collection of unique elements.

 |

 |  Methods defined here:

 |

 |  __and__(self, value, /)

 |      Return self&value.

 |

 |  __contains__(...)

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

 |

 |  __eq__(self, value, /)

 |      Return self==value.

 |

 |  __ge__(self, value, /)

 |      Return self>=value.

 |

 |  __getattribute__(self, name, /)

 |      Return getattr(self, name).

 |

 |  __gt__(self, value, /)

 |      Return self>value.

 |

 |  __iand__(self, value, /)

 |      Return self&=value.

 |

 |  __init__(self, /, *args, **kwargs)

 |      Initialize self.  See help(type(self)) for accurate signature.

 |

 |  __ior__(self, value, /)

 |      Return self|=value.

 |

 |  __isub__(self, value, /)

 |      Return self-=value.

 |

 |  __iter__(self, /)

 |      Implement iter(self).

 |

 |  __ixor__(self, value, /)

 |      Return self^=value.

 |

 |  __le__(self, value, /)

 |      Return self<=value.

 |

 |  __len__(self, /)

 |      Return len(self).

 |

 |  __lt__(self, value, /)

 |      Return self<value.

 |

 |  __ne__(self, value, /)

 |      Return self!=value.

 |

 |  __new__(*args, **kwargs) from builtins.type

 |      Create and return a new object.  See help(type) for accurate signature.

 |

 |  __or__(self, value, /)

 |      Return self|value.

 |

 |  __rand__(self, value, /)

 |      Return value&self.

 |

 |  __reduce__(...)

 |      Return state information for pickling.

 |

 |  __repr__(self, /)

 |      Return repr(self).

 |

 |  __ror__(self, value, /)

 |      Return value|self.

 |

 |  __rsub__(self, value, /)

 |      Return value-self.

 |

 |  __rxor__(self, value, /)

 |      Return value^self.

 |

 |  __sizeof__(...)

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

 |

 |  __sub__(self, value, /)

 |      Return self-value.

 |

 |  __xor__(self, value, /)

 |      Return self^value.

 |

 |  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

　　集合分类：可变集合、不可变集合

　　可变集合(set)：可添加和删除元素，非可哈希的，不能用作字典的键，也不能做其它集合的元素。

　　不可变集合(fromzenset)：与上面的恰恰相反

一、集合的相关操作

　　1. 创建集合

　　　　由于集合没有自己的语法格式，只能通过集合的工厂方法set()和frozenset()创建。创建集合仅有上述一种方法。

>>> s1 = set([1,2,2,3,4])

>>> s2 = frozeset([1,2,2,3,4])

>>> s2 = frozenset([1,2,2,3,4])

>>> s1

{1, 2, 3, 4}

>>> s2

frozenset({1, 2, 3, 4})

　　2. 访问集合

　　由于集合本身是无序的，所以不能为集合创建索引或切片操作，只能循环遍历或使用in、not in来访问或判断集合元素。

　　3. 更新集合

　　更新集合主要有下述三种方法

s.add()
s.update() # 更新多个元素
s.remove()

使用del关键字删除整个集合

　　4. 集合类型操作符

in ,not in
集合等价不等价(==, !=)
子集和超集
联合(取并集)
- 联合(union)操作与集合的or操作其实等价的，联合符号有个等价的方法，union()。
- ```
>>> a = set([1,2,3])

>>> b = set([4,5,6])

>>> a | b

{1, 2, 3, 4, 5, 6}   
```
交集
- 等价于intersection()方法

>>> a = set([1,2,3,4])

>>> b = set([3,4,5,6])

>>> a & b

{3, 4}

差集

　　等价于difference方法

```
>>> a

{1, 2, 3, 4}

>>> b

{3, 4, 5, 6}

>>> a - b

{1, 2}
```
>>> a.difference(b)
{1, 2}
对称差集
- 反向交集，对称差分是集合的XOR(‘异或’)，取得的元素属于s1,s2但不同时属于s1和s2.其等价方法symmetric_difference()
- ```
>>> a ^ b

{1, 2, 5, 6}

>>> a.symmetric_difference(b)

{1, 2, 5, 6}
```

巴特西

python3【基础】-集合

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