Anudocs :
I have a string which can be :
X=Y
or
X
Here X and Y can be any word containing alphabets.
I want that when string is X=Y then X should in group 1 and Y in group 2
but when string is X then X should be in group 2.
So far I am able to get only this :
(\w+)=(\w+)
What should be the right regex for it?
Wiktor Stribiżew :
To match alphabets, you need to use [a-zA-Z] (to match any ASCII letter) or [^\W\d_] (this matches any Unicode letter), not \w that matches letters, digits or underscores and some more chars by default in Python 3.x.
You need
^(?:([A-Za-z]+)=)?([A-Za-z]+)$
Or
^(?:([A-Za-z]+)=)?([A-Za-z]+)\Z
See the regex demo
Details
^- start of string(?:([A-Za-z]+)=)?- an optional non-capturing group matching 1 or 0 occurrences of:([A-Za-z]+)- Group 1: one or more letters=- a=char
([A-Za-z]+)- Group 2: one or more letters\Z- the very end of string ($matches the end of string position).