Python字典dictionary changed size during iteration
原因：字典一边遍历一边修改
>>> a = {1:0, 2:0, 3:1, 4:1}
>>> for i in a:
... a.pop(i)
...
0
Traceback (most recent call last):
File "", line 1, in
RuntimeError: dictionary changed size during iteration
>>> for i in a.keys():
... a.pop(i)
...
0
Traceback (most recent call last):
File "", line 1, in
RuntimeError: dictionary changed size during iteration
>>> for i in list(a.keys()):
... a.pop(i)
...
1
1