How to get index of specific group of character in python using regex

Question

Iam trying to get all the indexes of specific group of special character ,but my regex is returning the index of single character of that group,

here is my code:-

a=re.finditer(r"[/ \\][\\ /]","/ \\ / \\ / \\ / /")
print([m.start(0) for m in a])

its returning [0,2,4,6,8,10,12]

but i want [0,2,4,6,8,10] , i only want index of "/ \" and "\ /"

Then try re.finditer(r"(/) (\\)|(\\) (/)", "/ \\ / \\ / \\") and grab the appropriate group start() values. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Mar 30, 2018 at 15:05

Wiktor Stribiżew · Accepted Answer · 2018-03-30 15:09:19Z

1

You should remove the character class brackets and wrap each symbol with a capturing group. Then, you may use some logic to grab the indices of the groups that matched.

import re
res = []
for m in re.finditer(r"(/) (\\)|(\\) (/)", "/ \\ / \\ / \\"):
    if m.group(1):
        res.extend([m.start(1), m.start(2)])
    else:
        res.extend([m.start(3), m.start(4)])

print(res) # => [0, 2, 4, 6, 8, 10]

See the online Python demo.

Here, if Group 1 matched, that means we need to grab the start indices of Group 1 and 2, else, the start indices of Group 3 and 4.

answered Mar 30, 2018 at 15:09

Wiktor Stribiżew

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2 Comments

Abhishek Kumar Over a year ago

nah it ain't returning the correct output, can u check it with string "/ \\ / \\ / \\ / /" ,its printing [0,4,8]

Wiktor Stribiżew Over a year ago

@AbhishekKumar It prints [0, 2, 4, 6, 8, 10]

Abhishek Kumar · Accepted Answer · 2018-03-30 15:19:17Z

0

I found an better answer for that, its short one liner

print([m.start(0) for m in re.finditer(r"(?=(/ \\|\\ /))", "/ \\ / \\ / \\ / /")])

answered Mar 30, 2018 at 15:19

Abhishek Kumar

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