Difference Of Squares in Python
Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
1  exercism fetch python differenceofsquares

Difference Of Squares
Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
The square of the sum of the first ten natural numbers is (1 + 2 + ... + 10)² = 55² = 3025.
The sum of the squares of the first ten natural numbers is 1² + 2² + ... + 10² = 385.
Hence the difference between the square of the sum of the first ten natural numbers and the sum of the squares of the first ten natural numbers is 3025  385 = 2640.
Exception messages
Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include a message.
To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
raise Exception
, you should write:
1 
raise Exception("Meaningful message indicating the source of the error")

Running the tests
To run the tests, run the appropriate command below (why they are different):
 Python 2.7:
py.test difference_of_squares_test.py
 Python 3.3+:
pytest difference_of_squares_test.py
Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
python m pytest difference_of_squares_test.py
Common pytest
options

v
: enable verbose output 
x
: stop running tests on first failure 
ff
: run failures from previous test before running other test cases
For other options, see python m pytest h
Submitting Exercises
Note that, when trying to submit an exercise, make sure the solution is in the $EXERCISM_WORKSPACE/python/differenceofsquares
directory.
You can find your Exercism workspace by running exercism debug
and looking for the line that starts with Workspace
.
For more detailed information about running tests, code style and linting, please see the help page.
Source
Problem 6 at Project Euler http://projecteuler.net/problem=6
Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.