LGTM: Start testing on Python 3 instead of Python 2

[cclauss]

Fixes: #492

Tests for the issues raised in #485, #486, and #500

Ready for review. @harshildarji @ParthS007 @AlexDvorak

[harshildarji]

@cclauss All checks failed! The LGTM extraction log says undefined name 'raw_input' in several files. I think we will have to update all those files. People imported print_function from __future__ as:

from __future__ import print_function

but did not bothered to write:

try:
    raw_input             # Python 2
except NameError:
    raw_input = input     # Python 3

[AlexDvorak]

i’ll change the .lgtm.yml in #500 so that all tests will pass then this can be closed or merged

[cclauss]

@harshildarji Yes... Those issues were created in one merged pull request. https://github.com/TheAlgorithms/Python/pull/483/files @AlexDvorak is busy fixing them in #500

[harshildarji]

@cclauss I can revert the PR #483! But as you said @AlexDvorak is working on it, I won't revert it, otherwise it may cause conflicts (I think).

[AlexDvorak]

so is this PR going to get merged as #500 is already merged?

[cclauss]

We need #486 to land first. Also a raw_int fix.

[harshildarji]

@cclauss I've corrected raw_int and also that get_ipython thing! So I think this time there will be no errors!