Question

I can’t find how to proceed for a regular expression, here is an example:

string = "red\\/banana 36    monkey\\/apple 14   red\\/apple 23  red\\/horse 56  bull\\/red 67  monkey\\/red 45    bull\\/shark 89"

I want to do a single regex with re.match.group() which will take into account only the ones like red/xxxx and the ones like xxxx/red and group the xxxx names only, not couples:

I want to do:

print(match.group("beginningwithred") + " " + match.group("number")

and obtain:

banana 36
apple 23
horse 56

then do:

print(match.group("endingwithred") + " " + match.group("number")

and obtain:

bull 67
monkey 45

my current code goes like:

iterator = regex.finditer(string)
for match in iterator:
    regex = re.compile('red\\\\\\\\/(?P<beginningwithred>banana|apple|horse)|(?P<endingwithred>bull|monkey)\\\\\\\\/red (?P<number>\d\d)')

but it doesn’t work, I can’t use | between groups and python HOWTO doesn’t help..
I tried with { } too including the whole two expressions but it doesn’t work either.
It must not be really complicated but I can’t find out what’s wrong.

Answer 1

i don’t completely follow, but it sounds like you want non-capturing groups around your alternatives:

(?:foo|bar|baz)

that lets you use | without creating a “real” group.

---

update why doesn’t this help? is this not right?

>>> s="red\\/banana 36    monkey\\/apple 14   red\\/apple 23  red\\/horse 56  bull\\/red 67  monkey\\/red 45    bull\\/shark 89"
>>> r = re.compile(r'(?:red\\/(?P<begin>\w+)|(?P<end>\w+)\\/red)\s+(?P<number>\d+)')
>>> for m in r.finditer(s):
...     print(m.groups())

('banana', None, '36')
('apple', None, '23')
('horse', None, '56')
(None, 'bull', '67')
(None, 'monkey', '45')

---

update2

if you just want to print out the non-None values you can do something like:

  >>> for m in r.finditer(s):
  ...     print(','.join(g for g in m.groups() if g is not None))