fengfeng@fengfeng-Lenovo-XiaoXin-700-15ISK:~$ cat -n test1.py
1 a = 1
2 def do_something():
3 print a
4
5 do_something()
fengfeng@fengfeng-Lenovo-XiaoXin-700-15ISK:~$ python test1.py
1
fengfeng@fengfeng-Lenovo-XiaoXin-700-15ISK:~$ cat -n test2.py
1 a = 1
2 def do_something():
3 print a
4 a = 3
5
6 do_something()
fengfeng@fengfeng-Lenovo-XiaoXin-700-15ISK:~$ python test2.py
Traceback (most recent call last):
File "test2.py", line 6, in <module>
do_something()
File "test2.py", line 3, in do_something
print a

UnboundLocalError: local variable 'a' referenced before assignment

为什么test2.py给a赋了一个值就出错了呢？