So I have this regex:

(^(\s+)?(?P<NAME>(\w)(\d{7}))((01f\.foo)|(\.bar|\.goo\.moo\.roo))$|(^(\s+)?(?P<NAME2>R1_\d{6}_\d{6}_)((01f\.foo)|(\.bar|\.goo\.moo\.roo))$))

Now if I try and do a match against this:

B048661501f.foo

I get this error:

  File "C:\Python25\lib\re.py", line 188, in compile
    return _compile(pattern, flags)
  File "C:\Python25\lib\re.py", line 241, in _compile
    raise error, v # invalid expression
sre_constants.error: redefinition of group name 'NAME' as group 9; was group 3

If I can't define the same group twice in the same regex expression for two different cases, what do I do?

No, you can't have two groups of the same name, this would somehow defy the purpose, wouldn't it?

What you probably really want is this:

^\s*(?P<NAME>\w\d{7}|R1_(?:\d{6}_){2})(01f\.foo|\.(?:bar|goo|moo|roo))$

I refactored your regex as far as possible. I made the following assumptions:

You want to (correct me if I'm wrong):

• ignore white space at the start of the string
• match either of the following into a group named "NAME":
  • a letter followed by 7 digits, or
  • "R1_", and two times (6 digits + "_")
• followed by either:
  • "01f.foo" or
  • "." and ("bar" or "goo" or "moo" or "roo")
• followed by the end of the string

You could also have meant:

^\s*(?P<NAME>\w\d{7}01f|R1_(?:\d{6}_){2})\.(?:foo|bar|goo|moo|roo)$

Which is:

• ignore white space at the start of the string
• match either of the following into a group named "NAME":
  • a letter followed by 7 digits and "01f"
  • "R1_", and two times (6 digits + "_")
• a dot
• "foo", "bar", "goo", "moo" or "roo"
• the end of the string