Question

I’m trying to parse a string with unknown number of elements with RegEx in Python. Here is the example:

>>>> import re
>>>> re.match("\=( A([0-9]+))*", "= A1 A2 A3 A4").groups()[1::2]
('4',)

I expect to have:

('1', '2', '3', '4',)

How can I get the expected result?

EDIT:

re.findall will not work for me. Let me make a better example:

I want to match the following string:

_func(cmd, param1, param2, param3, param4)_

I don’t know in advance the nummber of parameters. I expected to solve it using the following code:

>>> re.match("(\w+)\(cmd(, (\w+))*\)", "func(cmd, param1, param2, param3, param4)")

But this do not work, since groups ()* are not expanded to many items, but only last is used. Any ideas?

Answer 1

pat = re.compile(r' A(\d+)')
lst = re.findall(pat, "= A1 A2 A3 A4")

This returns a list, and in your example you showed a tuple. I presume a list will work for you, but of course you can always do:

t = tuple(lst)

The answer I just gave doesn’t actually check for the = in the input string. If you need to do that, you can always use two patterns and two steps:

pat0 = re.compile(r'=(?: A\d+)+')
pat1 = re.compile(r' A(\d+)')

m = pat0.search("= A1 A2 A3 A4")
if not m:
    print("input string not what was expected")
else:
    s = m.group(0)
    lst = re.findall(pat, s)

EDIT: Code that handles your func() example:

s_code = "func(cmd, param1, param2, param3, param4)"
pat_recognize_args = re.compile(r'func\(cmd([^)]*)\)')
pat_parse_args = re.compile(r'[, ]+([^, ]+)')

m = pat_recognize_args.search(s_code)
if m:
    s = m.group(1)
    lst = re.findall(pat_parse_args, s)

When I ran the above code, lst was set to: ['param1', 'param2', 'param3', 'param4']

pat_recognize_args looks for the literal string func with a literal ( (which is backslash-escaped in the pattern so re won’t try to use it to start a match group), then the literal string cmd, and then a match group that matches anything up to a literal ) character; then the match group is closed with a ) and a literal ) is there to match the actual ) that finishes the function call. After this pattern matches, the match object will have group 1 set to just the interesting arguments from the function call.

So next we set s = m.group(1) and then have re.findall() pull out the arguments for us.