Tab Error in Python

Question

The following python code throws this error message, and I can't tell why, my tabs seem to be in line:

File "test.py", line 12
    pass
       ^ TabError: inconsistent use of tabs and spaces in indentation

My code:

class eightPuzzle(StateSpace):
    StateSpace.n = 0

    def __init__(self, action, gval, state, parent = None):
        StateSpace.__init__(self, action, gval, parent)
        self.state = state

    def successors(self) :
        pass

Answer 1

You cannot mix tabs and spaces, according the PEP8 styleguide:

Spaces are the preferred indentation method.

Tabs should be used solely to remain consistent with code that is already indented with tabs.

Python 3 disallows mixing the use of tabs and spaces for indentation.

Python 2 code indented with a mixture of tabs and spaces should be converted to using spaces exclusively.

When invoking the Python 2 command line interpreter with the -t option, it issues warnings about code that illegally mixes tabs and spaces. When using -tt these warnings become errors. These options are highly recommended!

Answer 2

not using the backspace also is important (especially in the Leafpad editor). If you want to decrease indent, use only Alt_key + TAB.

This should be done when you delete a line in a Python code.

Answer 3

open your code in a text editor, highlight all of it (ctr+a) and go to format and select either "Tabify region" or "Untabify region". It'll just make all the indents have the same format.