Simple Pythonista utility script that you need to put this Pythonista Actions menu. It goes though the script currently open in the Pythonista Editor, converting all tab characters ('\t') into four space characters.

tabsTo4Spaces.py

# replace ALL tab characters with four spaces

import editor, sys

theText = editor.get_text()
theCount = theText.count('\t')
if not theText.count('\t'):
    print('no tabs found.')
    sys.exit()
theLength = len(theText)
theText = theText.splitlines()
#theSelection = editor.get_selection()
for i in range(len(theText)):
    theText[i] = theText[i].replace('\t', '    ')
editor.replace_text(0, theLength, '\n'.join(theText))
#editor.set_selection(theSelection[0])