assert first_char_set - second_char_set == {'r', 'd', 'b'} to assert first_char_set - second_char_set == {'r', 'b', 'd'}

* Fix test_glob

== operator for lists relies on the order of elements in the list. cmp() does not.
In my case, on Linux Mint, python3.6 glob() returned list had items in reverse order then expected in the test.
The glob() doc doesn't specify specific ordering.
cmp() for list objects doesn't rely on the order of items and produces the right result.

* Use python3

* Travis CI: Add flake8 to the testing 

Add [flake8](http://flake8.pycqa.org) tests to find Python syntax errors and undefined names.

__E901,E999,F821,F822,F823__ are the "_showstopper_" flake8 issues that can halt the runtime with a SyntaxError, NameError, etc. Most other flake8 issues are merely "style violations" -- useful for readability but they do not effect runtime safety.
* F821: undefined name `name`
* F822: undefined name `name` in `__all__`
* F823: local variable name referenced before assignment
* E901: SyntaxError or IndentationError
* E999: SyntaxError -- failed to compile a file into an Abstract Syntax Tree

* learn-python should not teach the antipattern of bare exceptions

See PEP8 and https://realpython.com/the-most-diabolical-python-antipattern

* noqa F821 - We are intentionally raising NameError

* Two consecutive blank lines before a function definition

* flake8 --max-complexity=10 --> 12

* pylint: disable=broad-except

* Update test_tuples.py

* Update test_tuples.py

Fixed code style issues. (Trailing whitespace, blank line whitespace and line length too long)

* Update test_tuples.py

* Update test_tuples.py

* Update test_tuples.py

* Update test_tuples.py

* pep8 compliant

changed "you're" to "you"

* Added simple descriptions to files missing descriptions at the top of the files.

Added simple descriptions/summary for test_class_objects.py, test_inheritance.py, test_method_objects.py, test_multiple_inheritance.py, test_file_methdos.py, test_file_reading.py, test_math.py

* removed trailing spaces