local.py

Python 2.7.10 (default, Sep  7 2015, 13:51:49) 
[GCC 5.2.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 1
>>> def aa():
...   print(a)
... 
>>> aa()
1
>>> def aa():
...   print(a)
...   a = a + 1
... 
>>> aa()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in aa
UnboundLocalError: local variable 'a' referenced before assignment