series.py mathematical series

Exceptions (SyntaxError, TypeError, NameError and AttributionError)
I can see what you're going for, but with these assert statements, but it doesn't quite work as you expect. The if ``if __name__ == '__main__':`` block is only executed if the Python file is being ran. If we run the file, what's the value bound to `a`? 
  
Assert statements should demonstrate that your functions work as advertised. Meaning that your functions produce accurate and expected outputs for a range of inputs.

Something like:

     if __name__ == "__main__":
     # assert function(input) == expected
     ...
     assert fibonacci(7) == 13
     ...
     assert lucas(4) == 7
     ...
     assert sum_series(4, 2, 1) == lucas(4)
     ...
     print('all tests passed!')