I just pulled from a git repo where the users are on Python 2. My system is running Python 3 and with no changes in the code, I am getting this error:
TabError: inconsistent use of tabs and spaces in indentation
Exists a command
Convert all tabs in region to multiple spaces, preserving columns. If called interactively with prefix ARG, convert for the entire buffer.
I.e. call it with C-u to convert all TABs in buffer.
As comment points out correctly:
tabify does the inverse, converts multiple spaces to tabs - while using spaces seems a common convention not just in Python.