From c3f7675134b04bff4e406449592a68b02fc15be1 Mon Sep 17 00:00:00 2001 From: Dmitry Kokorin Date: Thu, 10 Jun 2021 19:38:18 +0300 Subject: [PATCH] Python: luhn --- python/luhn/.exercism/metadata.json | 1 + python/luhn/README.md | 112 ++++++++++++++++++++++++++++ python/luhn/luhn.py | 30 ++++++++ python/luhn/luhn_test.py | 75 +++++++++++++++++++ 4 files changed, 218 insertions(+) create mode 100644 python/luhn/.exercism/metadata.json create mode 100644 python/luhn/README.md create mode 100644 python/luhn/luhn.py create mode 100644 python/luhn/luhn_test.py diff --git a/python/luhn/.exercism/metadata.json b/python/luhn/.exercism/metadata.json new file mode 100644 index 0000000..3add0a7 --- /dev/null +++ b/python/luhn/.exercism/metadata.json @@ -0,0 +1 @@ +{"track":"python","exercise":"luhn","id":"5daf06c1ba214c66a86767020db309e9","url":"https://exercism.io/my/solutions/5daf06c1ba214c66a86767020db309e9","handle":"DmitryKokorin","is_requester":true,"auto_approve":false} \ No newline at end of file diff --git a/python/luhn/README.md b/python/luhn/README.md new file mode 100644 index 0000000..cde1cca --- /dev/null +++ b/python/luhn/README.md @@ -0,0 +1,112 @@ +# Luhn + +Given a number determine whether or not it is valid per the Luhn formula. + +The [Luhn algorithm](https://en.wikipedia.org/wiki/Luhn_algorithm) is +a simple checksum formula used to validate a variety of identification +numbers, such as credit card numbers and Canadian Social Insurance +Numbers. + +The task is to check if a given string is valid. + +Validating a Number +------ + +Strings of length 1 or less are not valid. Spaces are allowed in the input, +but they should be stripped before checking. All other non-digit characters +are disallowed. + +## Example 1: valid credit card number + +```text +4539 1488 0343 6467 +``` + +The first step of the Luhn algorithm is to double every second digit, +starting from the right. We will be doubling + +```text +4_3_ 1_8_ 0_4_ 6_6_ +``` + +If doubling the number results in a number greater than 9 then subtract 9 +from the product. The results of our doubling: + +```text +8569 2478 0383 3437 +``` + +Then sum all of the digits: + +```text +8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80 +``` + +If the sum is evenly divisible by 10, then the number is valid. This number is valid! + +## Example 2: invalid credit card number + +```text +8273 1232 7352 0569 +``` + +Double the second digits, starting from the right + +```text +7253 2262 5312 0539 +``` + +Sum the digits + +```text +7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57 +``` + +57 is not evenly divisible by 10, so this number is not valid. + + +## 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 `pytest luhn_test.py` + +Alternatively, you can tell Python to run the pytest module: +`python -m pytest luhn_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/luhn` 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 + +The Luhn Algorithm on Wikipedia [http://en.wikipedia.org/wiki/Luhn_algorithm](http://en.wikipedia.org/wiki/Luhn_algorithm) + +## Submitting Incomplete Solutions + +It's possible to submit an incomplete solution so you can see how others have completed the exercise. diff --git a/python/luhn/luhn.py b/python/luhn/luhn.py new file mode 100644 index 0000000..dccc5bd --- /dev/null +++ b/python/luhn/luhn.py @@ -0,0 +1,30 @@ +import re + +class Luhn: + def __init__(self, card_num): + + pattern = re.compile(r'\s+') + card_num = re.sub(pattern, '', card_num) + + if not card_num.isnumeric() or len(card_num) < 2: + self.is_valid = False + else: + + checksum = 0 + + for i, ch in enumerate(reversed(card_num)): + + x = int(ch) + + if i % 2: + x *= 2 + + if x > 9: + x -= 9 + + checksum += x + + self.is_valid = not (checksum % 10) + + def valid(self): + return self.is_valid diff --git a/python/luhn/luhn_test.py b/python/luhn/luhn_test.py new file mode 100644 index 0000000..e22f851 --- /dev/null +++ b/python/luhn/luhn_test.py @@ -0,0 +1,75 @@ +import unittest + +from luhn import Luhn + +# Tests adapted from `problem-specifications//canonical-data.json` + + +class LuhnTest(unittest.TestCase): + def test_single_digit_strings_can_not_be_valid(self): + self.assertIs(Luhn("1").valid(), False) + + def test_a_single_zero_is_invalid(self): + self.assertIs(Luhn("0").valid(), False) + + def test_a_simple_valid_sin_that_remains_valid_if_reversed(self): + self.assertIs(Luhn("059").valid(), True) + + def test_a_simple_valid_sin_that_becomes_invalid_if_reversed(self): + self.assertIs(Luhn("59").valid(), True) + + def test_a_valid_canadian_sin(self): + self.assertIs(Luhn("055 444 285").valid(), True) + + def test_invalid_canadian_sin(self): + self.assertIs(Luhn("055 444 286").valid(), False) + + def test_invalid_credit_card(self): + self.assertIs(Luhn("8273 1232 7352 0569").valid(), False) + + def test_invalid_long_number_with_an_even_remainder(self): + self.assertIs(Luhn("1 2345 6789 1234 5678 9012").valid(), False) + + def test_valid_number_with_an_even_number_of_digits(self): + self.assertIs(Luhn("095 245 88").valid(), True) + + def test_valid_number_with_an_odd_number_of_spaces(self): + self.assertIs(Luhn("234 567 891 234").valid(), True) + + def test_valid_strings_with_a_non_digit_added_at_the_end_become_invalid(self): + self.assertIs(Luhn("059a").valid(), False) + + def test_valid_strings_with_punctuation_included_become_invalid(self): + self.assertIs(Luhn("055-444-285").valid(), False) + + def test_valid_strings_with_symbols_included_become_invalid(self): + self.assertIs(Luhn("055# 444$ 285").valid(), False) + + def test_single_zero_with_space_is_invalid(self): + self.assertIs(Luhn(" 0").valid(), False) + + def test_more_than_a_single_zero_is_valid(self): + self.assertIs(Luhn("0000 0").valid(), True) + + def test_input_digit_9_is_correctly_converted_to_output_digit_9(self): + self.assertIs(Luhn("091").valid(), True) + + def test_using_ascii_value_for_non_doubled_non_digit_isn_t_allowed(self): + self.assertIs(Luhn("055b 444 285").valid(), False) + + def test_using_ascii_value_for_doubled_non_digit_isn_t_allowed(self): + self.assertIs(Luhn(":9").valid(), False) + + # Additional tests for this track + + def test_is_valid_can_be_called_repeatedly(self): + # This test was added, because we saw many implementations + # in which the first call to valid() worked, but the + # second call failed(). + number = Luhn("055 444 285") + self.assertIs(number.valid(), True) + self.assertIs(number.valid(), True) + + +if __name__ == "__main__": + unittest.main()