Question

Here it is:

import re
>>>s = 'abc -j k -l m'
>>>m = re.search('-\w+ \w+', s)
>>>m.groups()
()
>>> m.group(0)
'-j k'

Why groups() gives me nothing, but group(0) yields some? What is the difference?

Follow Up

Code is as follows

>>>re.findall('(-\w+ \w+)', s)
['-j k', '-l m', '-n o']

findall can get me all the -\w+ \w+ substrings, but look at this:

>>>m = re.search('(-\w+ \w+)+', s)
>>>m.groups()
('-j k',)

Why can’t search give me all the substrings?

Follow Up Again

If s = 'abc -j k -l m -k o, and

>>>m = re.search(r'(-\w+ \w+ )+', s)
>>>m.groups()
('-l m ',)      # why just one substring?
>>>m.group(0)
'-j k -l m '    # as I expected

Answer 1

groups() only returns any explicitly-captured groups in your regex (denoted by ( round brackets ) in your regex), whereas group(0) returns the entire substring that’s matched by your regex regardless of whether your expression has any capture groups.

The first explicit capture in your regex is indicated by group(1) instead.

Re follow-up edit:

Why can’t search give me all the substrings?

search() will only return the first match against the pattern in your input string.