三元运算又叫三目运算，是对简单的条件语句的缩写。
书写格式：
n1 = 值1 if 条件 else 值2 # 如果条件成立，那么将 “值1” 赋值给n1变量，否则，将“值2”赋值给n1变量
基本数据类型之set：
set集合，是一个无序且不重复的元素集合。
set和dict类似，也是一组key的集合，但是它不存储value，由于key不能重复，所以在set中没有重复的key。
要创建一个set，需要提供一个list作为输入集合：
s = set([1, 2, 3])
print(s)
{1, 2, 3}
class set(object): """ set() -> new empty set object set(iterable) -> new set object Build an unordered collection of unique elements. """ def add(self, *args, **kwargs): # real signature unknown """ Add an element to a set，添加元素 This has no effect if the element is already present. """ pass def clear(self, *args, **kwargs): # real signature unknown """ Remove all elements from this set. 清楚内容""" pass def copy(self, *args, **kwargs): # real signature unknown """ Return a shallow copy of a set. 浅拷贝 """ pass def difference(self, *args, **kwargs): # real signature unknown """ Return the difference of two or more sets as a new set. A中存在，B中不存在 (i.e. all elements that are in this set but not the others.) """ pass def difference_update(self, *args, **kwargs): # real signature unknown """ Remove all elements of another set from this set. 从当前集合中删除和B中相同的元素""" pass def discard(self, *args, **kwargs): # real signature unknown """ Remove an element from a set if it is a member. If the element is not a member, do nothing. 移除指定元素，不存在不保错 """ pass def intersection(self, *args, **kwargs): # real signature unknown """ Return the intersection of two sets as a new set. 交集 (i.e. all elements that are in both sets.) """ pass def intersection_update(self, *args, **kwargs): # real signature unknown """ Update a set with the intersection of itself and another. 取交集并更更新到A中 """ pass def isdisjoint(self, *args, **kwargs): # real signature unknown """ Return True if two sets have a null intersection. 如果没有交集，返回True，否则返回False""" pass def issubset(self, *args, **kwargs): # real signature unknown """ Report whether another set contains this set. 是否是子序列""" pass def issuperset(self, *args, **kwargs): # real signature unknown """ Report whether this set contains another set. 是否是父序列""" pass def pop(self, *args, **kwargs): # real signature unknown """ Remove and return an arbitrary set element. Raises KeyError if the set is empty. 移除元素 """ pass def remove(self, *args, **kwargs): # real signature unknown """ Remove an element from a set; it must be a member. If the element is not a member, raise a KeyError. 移除指定元素，不存在保错 """ pass def symmetric_difference(self, *args, **kwargs): # real signature unknown """ Return the symmetric difference of two sets as a new set. 对称交集 (i.e. all elements that are in exactly one of the sets.) """ pass def symmetric_difference_update(self, *args, **kwargs): # real signature unknown """ Update a set with the symmetric difference of itself and another. 对称交集，并更新到a中 """ pass def union(self, *args, **kwargs): # real signature unknown """ Return the union of sets as a new set. 并集 (i.e. all elements that are in either set.) """ pass def update(self, *args, **kwargs): # real signature unknown """ Update a set with the union of itself and others. 更新 """ pass