regex in python: how to use variable string in pattern?

Question

I can match a string from a list of string, like this:

keys = ['a', 'b', 'c']
for key in keys:
    if re.search(key, line):
       break

the problem is that I would like to match a pattern made from regular expression + string that I would specify. Something like this:

keys = ['a', 'b', 'c']
for key in keys:
    if re.search('[^\[]'+key+'[^\]]', line):
       break

but this does not work (in this example I would like to match 'a', 'b' and 'c' only if they appear in squared brackets). I think this has to do with raw strings etc, but I cannot find a way to make it work. Suggestions?

EDIT:

let's say I want to match a pattern a bit more complicated:

'[^\s*data\.'+key+'\s*=\s*\[(.+)[^\]]'

in order to match the number in brackets:

 data.a =  [12343.232 ]

Then use `re.search(r'\[{}]'.format(key), line)`. Or `if r'[{}]'.format(key) in line:`. See https://ideone.com/UimIyJ — Wiktor Stribiżew, Jul 14 '16 at 13:14
"... I would like to match [...] if they appear in squared brackets" Then why have you negated the square brackets? — Ignacio Vazquez-Abrams, Jul 14 '16 at 13:15
what about if I want to match something more complicated? like in the edit I have made — simona, Jul 14 '16 at 13:15
@IgnacioVazquez-Abrams because I want to match only what appears in the brackets — simona, Jul 14 '16 at 13:18
Check https://ideone.com/bVDxvr - I think you want to match `a` only when inside brackets. In `data.a = [12343.232 ]`, it is outside, thus, no match is expected, right? And you want to match `a` inside `[data.a] = 12343.232`? — Wiktor Stribiżew, Jul 14 '16 at 13:20
The pattern from your update is very strange. Please make your question clearer, add more details on what you are trying to achieve. — Wiktor Stribiżew, Jul 14 '16 at 13:25
@IgnacioVazquez-Abrams you are right! I took the wrong pattern, but how do i match only the content in the brackets? — simona, Jul 14 '16 at 13:28

Nicolas Heimann · Accepted Answer · 2016-07-14T15:16:48.923

3

re.search('\['+re.escape(key)+']', line):

this will match [key]. Note that re.escape was added to prevent that characters within key are interpreted as regex.

edited Jul 14 '16 at 15:16

answered Jul 14 '16 at 13:22

Nicolas Heimann

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1

You do not need to escape `]`. – Wiktor Stribiżew Jul 14 '16 at 13:51
Thank for the hint, but, are you sure? What if key=abc, then the regex would be '[abc]' witch matches any a, b, or c? What do I miss here? – Nicolas Heimann Jul 14 '16 at 14:46
1

No, the `[` must be escaped, and `]` does not have to. – Wiktor Stribiżew Jul 14 '16 at 14:56

regex in python: how to use variable string in pattern?

1 Answers1