Python regex — extraneous matchings

Question

I want to split a string using -, +=, ==, =, +, and white-space as delimiters. I want to keep the delimiter

Answer 1

Why is it behaving this way?

According to the documentation for re.split:

If capturing parentheses are used in pattern, then the text of all groups in the pattern are also returned as part of the resulting list.

This is literally correct: if capturing parentheses are used, then the text of all groups are returned, whether or not they matched anything; the ones which didn't match anything return None.

As always with split, two consecutive delimiters are considered to separate empty strings, so you get empty strings interspersed.

how might I change it to get what I want?

The simplest solution is to filter the output:

filter(None, pattern.split(s))