No complaint about inconsistent indentation levels

[schmiddy]

pep8 neglects to complain about code with mismatched indentation levels, such as this snippet:

if True:
        print 'yes'
else:
    print 'no'

Example taken from a complaint about this problem on StackOverflow. pylint gives a reasonable error here, namely:

W: 2, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)

The PEP 8 standard says simply:

Use 4 spaces per indentation level.

And I would like to have a warning about any indentation level other than 4 spaces. Here's the beginning of a fix. I think these errors might need to be separated based on:

a. mixing different indentation levels, as in the example above
b. using any indentation level other than 4 spaces (including tabs)

IMO a.) should definitely be an error by default. I can see the case for b.) being off by default and/or just a warning, particularly since PEP 8 makes an allowance for tabs by saying:

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