Prime Factors in Python
Compute the prime factors of a given natural number.
1  exercism fetch python primefactors

Prime Factors
Compute the prime factors of a given natural number.
A prime number is only evenly divisible by itself and 1.
Note that 1 is not a prime number.
Example
What are the prime factors of 60?
 Our first divisor is 2. 2 goes into 60, leaving 30.
 2 goes into 30, leaving 15.
 2 doesn't go cleanly into 15. So let's move on to our next divisor, 3.
 3 goes cleanly into 15, leaving 5.
 3 does not go cleanly into 5. The next possible factor is 4.
 4 does not go cleanly into 5. The next possible factor is 5.
 5 does go cleanly into 5.
 We're left only with 1, so now, we're done.
Our successful divisors in that computation represent the list of prime factors of 60: 2, 2, 3, and 5.
You can check this yourself:
 2 * 2 * 3 * 5
 = 4 * 15
 = 60
 Success!
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 prime_factors_test.py
 Python 3.3+:
pytest prime_factors_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 prime_factors_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/primefactors
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
The Prime Factors Kata by Uncle Bob http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata
Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.