regex in python: how to use variable string in pattern? [duplicate]

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 ideone.com/UimIyJ — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jul 14, 2016 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
– Ignacio Vazquez-Abrams, Commented Jul 14, 2016 at 13:15
what about if I want to match something more complicated? like in the edit I have made — simona
– simona, Commented Jul 14, 2016 at 13:15
@IgnacioVazquez-Abrams because I want to match only what appears in the brackets — simona
– simona, Commented Jul 14, 2016 at 13:18

Nicolas Heimann · Accepted Answer · 2016-07-14 15:16:48Z

4

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, 2016 at 15:16

answered Jul 14, 2016 at 13:22

Nicolas Heimann

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3 Comments

Wiktor Stribiżew Over a year ago

You do not need to escape ].

Nicolas Heimann Over a year ago

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?

Wiktor Stribiżew Over a year ago

No, the [ must be escaped, and ] does not have to.

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