try except in python valueerror code example

Example 1: python file open try except error

def FileCheck(fn):
    try:
      open(fn, "r")
      return 1
    except IOError:
      print "Error: File does not appear to exist."
      return 0

result = FileCheck("testfile")
print result

Example 2: python defualt error handler

import sys
def my_except_hook(exctype, value, traceback):
    if exctype == KeyboardInterrupt:
        print "Handler code goes here"
    else:
        sys.__excepthook__(exctype, value, traceback)
sys.excepthook = my_except_hook