Regular Expression to match numbers in square brackets in python

Question

I need to match and return the string index of numbers which are contained in square brackets. Example string:

Gabrilovich and Markovitch [11, 12] propose a method to use conditional random fields [6] as a training process.....

Here I would like to extract the index of any given number like 11, 12 or 6 in the above case using regular expressions. I am trying

pattern = re.compile(r'[/11/]') # for 11
result =  re.search(pattern, text, flags=0)
print result.start()

However with this I am not getting desired results. Note: I would need a solution for matching the exact number I want, not any given number within brackets.

Answer 1

use this regex expression (\\[[,\\d\\s ]*)11([,\\d\\s ]*\\]) for retrieving all the 11's in the text

have a look at the example I uploaded https://regex101.com/r/lN8mA6/1

Answer 2

Since in Python we cannot use variable-width lookbehinds with standard re module, you can use capturing groups, and then check the index of the group.

Sample code for capturing 11 :

pattern = re.compile(r'(\[[^\]]*)\b(11)\b(?=[^\]]*\])') # for 11
text = 'Gabrilovich and Markovitch [11, 12] propose a method to use conditional random fields [6] as a training process.....'
result =  re.search(pattern, text)
if result:
    print result.start(2)

Result: 28 .

Note that I am using word boundaries around 11 to only match 11 , and not 111 or 112 .

Answer 3

Try this regexp: \\[\\s*(\\d*)(\\s*,\\s*(\\d*)\\s*)?(\\s*,\\s*(\\d*)\\s*)?(\\s*,\\s*(\\d*)\\s*)?(\\s*,\\s*(\\d*)\\s*)?(\\s*,\\s*(\\d*)\\s*)?(\\s*,\\s*(\\d*)\\s*)?\\] (the groups (\\s*,\\s*(\\d)\\s*)? are repeated to allow to get up to 7 numbers in between the square brackets) as this demo shows. If you want to be more general, you can substitute this regexp with \\[\\s*(\\d*)(\\s*,\\s*(\\d*)\\s*)*\\] that allows an indefinite number of numbers in the list (but then you will get the first and the last only in groups \\1 and \\3 )

If you use the first, you will allow spaces around the commas and you'll get the numbers in groups 1, 3, 5, 7, 11, 13 and 15.