Use regex to parse string into groups

Question

I cant seem to get regex to work with the following example. Basically I would like to parse 4 groups from a string such as below:

test.this
test[extra].this
test[extra].this{data}
test.this{data}

I would like to get the answer as such, for the examples above respectively:

val1='test', val2=None, val3='this', val4=None
val1='test', val2='extra', val3='this', val4=None
val1='test', val2='extra', val3='this', val4='data'
val1='test', val2=None, val3='this', val4='data'

I tried this but it's not working:

import re

tests = ["test.this",
         "test[extra].this",
         "test[extra].this{data}",
         "test.this{data}",]

for test in tests:
    m = re.match(r'^([^\[\.]+)(?:\[([^\]]+)])(?:\.([^{]+){)([^}]+)?$', test)
    if m:
        print(test, '->', m[1], m[2], m[3], m[4])

41686d6564 · Accepted Answer · 2020-09-15 05:22:14Z

2

If only the second and fourth groups are optional, you may use:

^([^\[\.]+)(?:\[([^\]]+)])?\.([^{\r\n]+)(?:{([^}\r\n]+)})?$

Demo.

Note that \r and \n were added in the negated character classes of the third and fourth groups to avoid going beyond the end of the line. If you're only using single-line strings, that won't be necessary.

edited Sep 15, 2020 at 5:22

answered Sep 15, 2020 at 5:17

41686d6564

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1 Comment

user1179317 Over a year ago

Yes this works, but yea I think you meant first and third is required, not optional. But yea this answer works. Will review your answer on how it works. Thanks!

Karan Raj · Accepted Answer · 2020-09-15 08:55:01Z

1

import re

tests = ["test.this",
     "test[extra].this",
     "test[extra].this{data}",
     "test.this{data}"]

pat = re.compile(r'(\w+)([\[])?(\w+)?([\]])?\.(\w+){?(\w+)?')
for test in tests:
    x = pat.search(test)
    print(x.group(1),x.group(3),x.group(5),x.group(6))

(\w+) -> captures test

([\[])? -> captures [

(\w+)? -> captures extra

([\]])? -> captures ]

(\w+) -> captures this

(\w+)? -> captures data

edited Sep 15, 2020 at 8:55

answered Sep 15, 2020 at 8:46

Karan Raj

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2 Comments

user1179317 Over a year ago

Question, how is '(\w+)?' not capturing '}' with data? I mean I know your solution works, just trying to understand how '}' is being ignored there

Karan Raj Over a year ago

contents inside the () braces are only captured in the grouping. since \w looks for only alphabets, digits, and underscores. Hence '}' is ignored.

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