eratosthenes prime test exercise

python/sieve/README.md

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+# Sieve
+
+Use the Sieve of Eratosthenes to find all the primes from 2 up to a given
+number.
+
+The Sieve of Eratosthenes is a simple, ancient algorithm for finding all
+prime numbers up to any given limit. It does so by iteratively marking as
+composite (i.e. not prime) the multiples of each prime, starting with the
+multiples of 2. It does not use any division or remainder operation.
+
+Create your range, starting at two and continuing up to and including the given limit. (i.e. [2, limit])
+
+The algorithm consists of repeating the following over and over:
+
+- take the next available unmarked number in your list (it is prime)
+- mark all the multiples of that number (they are not prime)
+
+Repeat until you have processed each number in your range.
+
+When the algorithm terminates, all the numbers in the list that have not
+been marked are prime.
+
+The wikipedia article has a useful graphic that explains the algorithm:
+https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+
+Notice that this is a very specific algorithm, and the tests don't check
+that you've implemented the algorithm, only that you've come up with the
+correct list of primes. A good first test is to check that you do not use
+division or remainder operations (div, /, mod or % depending on the
+language).
+
+## 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:
+
+```python
+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](https://github.com/pytest-dev/pytest/issues/1629#issue-161422224)):
+
+- Python 2.7: `py.test sieve_test.py`
+- Python 3.4+: `pytest sieve_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 sieve_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/sieve` 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 [Running the Tests](http://exercism.io/tracks/python/tests).
+
+## Source
+
+Sieve of Eratosthenes at Wikipedia [http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes](http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes)
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.