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118 lines
3.6 KiB
Markdown
118 lines
3.6 KiB
Markdown
# Book Store
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To try and encourage more sales of different books from a popular 5 book
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series, a bookshop has decided to offer discounts on multiple book purchases.
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One copy of any of the five books costs $8.
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If, however, you buy two different books, you get a 5%
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discount on those two books.
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If you buy 3 different books, you get a 10% discount.
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If you buy 4 different books, you get a 20% discount.
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If you buy all 5, you get a 25% discount.
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Note: that if you buy four books, of which 3 are
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different titles, you get a 10% discount on the 3 that
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form part of a set, but the fourth book still costs $8.
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Your mission is to write a piece of code to calculate the
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price of any conceivable shopping basket (containing only
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books of the same series), giving as big a discount as
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possible.
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For example, how much does this basket of books cost?
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- 2 copies of the first book
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- 2 copies of the second book
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- 2 copies of the third book
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- 1 copy of the fourth book
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- 1 copy of the fifth book
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One way of grouping these 8 books is:
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- 1 group of 5 --> 25% discount (1st,2nd,3rd,4th,5th)
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- +1 group of 3 --> 10% discount (1st,2nd,3rd)
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This would give a total of:
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- 5 books at a 25% discount
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- +3 books at a 10% discount
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Resulting in:
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- 5 x (8 - 2.00) == 5 x 6.00 == $30.00
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- +3 x (8 - 0.80) == 3 x 7.20 == $21.60
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For a total of $51.60
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However, a different way to group these 8 books is:
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- 1 group of 4 books --> 20% discount (1st,2nd,3rd,4th)
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- +1 group of 4 books --> 20% discount (1st,2nd,3rd,5th)
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This would give a total of:
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- 4 books at a 20% discount
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- +4 books at a 20% discount
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Resulting in:
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- 4 x (8 - 1.60) == 4 x 6.40 == $25.60
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- +4 x (8 - 1.60) == 4 x 6.40 == $25.60
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For a total of $51.20
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And $51.20 is the price with the biggest discount.
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## Exception messages
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Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
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indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not
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every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include
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a message.
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To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
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`raise Exception`, you should write:
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```python
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raise Exception("Meaningful message indicating the source of the error")
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```
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## Running the tests
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To run the tests, run the appropriate command below ([why they are different](https://github.com/pytest-dev/pytest/issues/1629#issue-161422224)):
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- Python 2.7: `py.test book_store_test.py`
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- Python 3.4+: `pytest book_store_test.py`
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Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
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`python -m pytest book_store_test.py`
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### Common `pytest` options
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- `-v` : enable verbose output
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- `-x` : stop running tests on first failure
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- `--ff` : run failures from previous test before running other test cases
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For other options, see `python -m pytest -h`
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## Submitting Exercises
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Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/book-store` directory.
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You can find your Exercism workspace by running `exercism debug` and looking for the line that starts with `Workspace`.
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For more detailed information about running tests, code style and linting,
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please see [Running the Tests](http://exercism.io/tracks/python/tests).
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## Source
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Inspired by the harry potter kata from Cyber-Dojo. [http://cyber-dojo.org](http://cyber-dojo.org)
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## Submitting Incomplete Solutions
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It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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