Python regex partial extract

Question

I want to find all data enclosed in [[ ]] these brackets.

[[aaaaa]] -> aaaaa

My python code (using re library) was

la = re.findall(r'\[\[(.*?)\]\]', fa.read())

What if I want to extract only 'a' from [[a|b]]

Any concise regular expression for this task? ( extract data before | )

Or should I use additional if statement?

Answer 1

You can try:

r'\[\[([^\]|]*)(?=.*\]\])'

([^\]|]*) will match until a | or ] is found. And (?=.*\]\]) is a lookahead to ensure that ]] is matched on RHS of match.

Testing:

>>> re.search( r'\[\[([^\]|]*)(?=.*\]\])', '[[aaa|bbb]]' ).group(1)
'aaa'
>>> re.search( r'\[\[([^\]|]*)(?=.*\]\])', '[[aaabbb]]' ).group(1)
'aaabbb'