Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.

For example, for the input '1027839564', the largest product for a series of 3 digits is 270 (9 * 5 * 6), and the largest product for a series of 5 digits is 7560 (7 * 8 * 3 * 9 * 5).

Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.

For the input '73167176531330624919225119674426574742355349194934', the largest product for a series of 6 digits is 23520.

Implementation note: In case of invalid inputs to the 'largest_product' function your program should raise a ValueError with a meaningful error message. Feel free to reuse your code from the 'series' exercise!

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:

raise Exception("Meaningful message indicating the source of the error")

To run the tests, run pytest largest_series_product_test.py

Alternatively, you can tell Python to run the pytest module: python -m pytest largest_series_product_test.py

• -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

Note that, when trying to submit an exercise, make sure the solution is in the $EXERCISM_WORKSPACE/python/largest-series-product 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.

A variation on Problem 8 at Project Euler http://projecteuler.net/problem=8

It's possible to submit an incomplete solution so you can see how others have completed the exercise.