A KeyError is raised when a value is not found as a key of a dictionary. The given code is rewritten as follows to catch the exception and find its type.
Example
import sys try: s = {'a':5, 'b':7}['c'] except: print (sys.exc_info())
Output
(<type 'exceptions.KeyError'>, KeyError('c',), <traceback object at 0x0000000003203748>)