Question

I’m using Python to parse a file in search for e-mail addresses, but I can’t figure out what the syntax for alternative regexps should be. Here’s the code:

addresses = []

pattern = '(\w+)@(\w+\.com)|(\w+)@(it.\w+\.com)'
for line in file:
    matches = re.findall(pattern,line)
    for m in matches:
        address = '%s@%s' % m
        addresses.append(address)

So I want to find addresses that look like [e-mail] or [e-mail], but the above code doesn’t work because either the first two groups are empty or the last two groups are empty. What is the correct solution? I need to use groups to store the user name (before @) and server name (after @) separately.

EDIT: Matching email adresses is only an example. What I’m trying to find out is how to match different regexps that have only one thing in common – they match two groups.

Answer 1

(\w+)@((?:it\.)?\w+\.com)

You want to capture the part after the @ whether it’s example.com or it.example.com, so you put both options inside the same capture group. But since they share a similar format, you can condense (it\.\w+\.com|\w+\.com) to just ((it\.)?\w+\.com)

The (?: ) makes that parens a non-capturing group, so it won’t take part in your matched groups. There will be one match for the first (\w+), and one match for the whole ((?:it\.)?\w+\.com) after the @. That’s two matches total, plus the default group-0 match for the full string.

EDIT: To answer your new question, all you have to do is follow the grouping I used, but stop before you condense it.
If your test cases are:

1) example@abcdef

2) example@123456

You could write your regex as such: (\w+)@([a-zA-Z]+|\d+), which would always have the part before the @ in group 1, and the part after in group 2. Notice that there are only two pairs of parens, and the |(“or”) operator appears inside of the second parens group.