Question

Given a string #abcde#jfdkjfd, how can I get the string between two # ? And I also want that if no # pair(means no # or only one #), the function will return None.

Answer 1

>>> import re
>>> s = "abc#def#ghi#jkl"
>>> re.findall(r"(?<=#)[^#]+(?=#)", s)
['def', 'ghi']

Explanation:

(?<=#)  # Assert that the previous character is a #
[^#]+   # Match 1 or more non-# characters
(?=#)   # Assert that the next character is a #