You can also raise an exception in your code, if you consider that the program should be interrupted:
if something_wrong: raise ExceptionYou can associate a message to the raise statement:
if something_wrong: raise Exception, " something went wrong"
Example 12.3. Raising an exception in case of a wrong DNA character
def check_dna(dna, alphabet='atgc'): """ using exceptions """ for base in dna: if base not in alphabet: raise ValueError, "%s not in %s" % (base, alphabet) return True