>>> from math import sqrt  
>>> exec "sqrt = 1"  
>>> sqrt(4)  
  
Traceback (most recent call last):  
  File "<pyshell#22>", line 1, in <module>  
    sqrt(4)  
TypeError: 'int' object is not callable  

>>> from math import sqrt  
>>> scope = {}  
>>> exec "sqrt = 1" in scope  
>>> sqrt(4)  
2.0