>>> import string
>>> import random
>>> string.ascii_letters[:random.randint(1,50)].title()
'Abcdefghijklmnopq'
>>> string.ascii_letters[:random.randint(1,50)].title()
'Abcdefghijklmnopqrstuvwxyzabcdefghijklmnopq'
>>> string.ascii_letters[:random.randint(1,50)].title()
'Abcdefghijklmnopqrs'

或者你可以使用itertools：

>>> import string
>>> import random
>>> from itertools import islice,cycle
>>> def randstr():
...     return ''.join(islice(cycle(string.ascii_lowercase),...                           random.randint(1,50))).title()
...
>>> randstr()
'Abcdefghijklmnopq'
>>> randstr()
'Abcdefghijklmnopqrstuvwxyzabcdefghijklmnopq'
>>> randstr()
'Abcdefghijklmnopqrs'