Code produces 'AttributeError' instead of correctly raising ValueError

Question

Using a regex expression, I am creating a function where certain criteria must be met (ex/ no white spaces allowed) and produces a tuple that is separated by a special character.

ex/ inputting a string of 'hello!world!hola' should produce a tuple of ('hello', 'world', 'hola').

I would like to raise a ValueError if the string does not meet my criteria. However, if the string does not meet my criteria, my code calls a AttributeError instead. Why is the function not properly calling the exception?

I tried to call a ValueError, but the function does not seem to catch my exception.

def produce_tupule (s):

    re_pair = re.compile(r'''^                        
                           ([a-zA-Z0-9._+-]+)
                           \!                            
                           ([a-zA-Z0-9._+-]+)
                           \!
                           ([a-zA-Z0-9._+-]+)
                           $              
                        ''',
                        re.VERBOSE)
    try:
        return (re_pair.match(s).groups())
    except ValueError as e:
        print(e)

I expect the output of produce_tupule('hello !world!hola') to result in the ValueError message since a whitespace exists in the string.

However, the error message points to the 'return:(re_pair.match(s).groups())' line and prints out an AttributeError: 'NoneType' object has no attribute 'groups'.

What is causing the function to not catch the exception and produce the AttributeError instead?

Perry · Accepted Answer · 2019-09-13 01:49:27Z

1

re.match returns None instead of raising a ValueError if the regular expression given fails to match your input. Your code then tries to access the .groups member of the None return value, which fails with an AttributeError.

If you want to raise a ValueError if the regular expression given fails to match, you have to do so explicitly by replacing your return (re_pair.match(s).groups()) line with code with explicit error checking:

match = re_pair.match(s)
if match is None:
    raise ValueError
return match.groups()

answered Sep 13, 2019 at 1:49

Perry

3,90326 gold badges40 silver badges51 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Code produces 'AttributeError' instead of correctly raising ValueError

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related