python 集合set中 add与update区别介绍

set(['hello','hello','hi'])
# {'hello', 'hi'}
set('hello hello hi')
# {' ', 'e', 'h', 'i', 'l', 'o'}

myset1 = set()
myset1.add('hello')
#{'hello'}
myset1.update('world')
#{'d', 'hello', 'l', 'o', 'r', 'w'}
myset2 = set()
myset2.add('123')
myset2.update('123')
#{'1', '123', '2', '3'}

a = set()
a.update([1]) #works
a.add(1) #works
a.update([1,2])#works
a.add([1,2])#fails 

set.add

>>> a = set()
>>> a.add(1)
>>> a
set([1])

>>> a.add([1, 2])
Traceback (most recent call last):
 File "<input>", line 1, in <module>
TypeError: unhashable type: 'list'

>>> a.update(1)
Traceback (most recent call last):
 File "<input>", line 1, in <module>
TypeError: 'int' object is not iterable

>>> a.update([1])
>>> a
set([1])

>>> set([1, 2]) | set([3, 4]) | set([1, 3])
set([1, 2, 3, 4])
>>> set([1, 2]) | set(range(3, 5)) | set(i for i in range(1, 5) if i % 2 == 1)
set([1, 2, 3, 4])

>>> a.update([1, 2], range(3, 5), (i for i in range(1, 5) if i % 2 == 1))
>>> a
set([1, 2, 3, 4])