(WIP) isbn-verifier: implement exercise

config.json

@@ -901,6 +901,21 @@
         "stacks"
       ]
     },
+    {
+      "uuid": "7961c852-c87a-44b0-b152-efea3ac8555c",
+      "slug": "isbn-verifier",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 3,
+      "topics": [
+        "type_conversion",
+        "conditionals",
+        "strings",
+        "arrays",
+        "integers",
+        "parsing"
+      ]
+    },
     {
       "uuid": "e7351e8e-d3ff-4621-b818-cd55cf05bffd",
       "slug": "accumulate",

exercises/isbn-verifier/README.md

@@ -0,0 +1,43 @@
+# Isbn Verifier
+
+Check if a given ISBN-10 is valid.
+
+## Functionality
+
+Given an unkown string the program should check if the provided string is a valid ISBN-10.
+Putting this into place requires some thinking about preprocessing/parsing of the string prior to calculating the check digit for the ISBN.
+
+The program should allow for ISBN-10 without the separating dashes to be verified as well.
+
+## ISBN
+
+Let's take a random ISBN-10 number, say `3-598-21508-8` for this.
+The first digit block indicates the group where the ISBN belongs. Groups can consist of shared languages, geographic regions or countries. The leading '3' signals this ISBN is from a german speaking country.
+The following number block is to identify the publisher. Since this is a three digit publisher number there is a 5 digit title number for this book.
+The last digit in the ISBN is the check digit which is used to detect read errors.
+
+The first 9 digits in the ISBN have to be between 0 and 9.
+The check digit can additionally be an 'X' to allow 10 to be a valid check digit as well.
+
+A valid ISBN-10 is calculated with this formula `(x1 * 10 + x2 * 9 + x3 * 8 + x4 * 7 + x5 * 6 + x6 * 5 + x7 * 4 + x8 * 3 + x9 * 2 + x10 * 1) mod 11 == 0`
+So for our example ISBN this means:
+(3 * 10 + 5 * 9 + 9 * 8 + 8 * 7 + 2 * 6 + 1 * 5 + 5 * 4 + 0 * 3 + 8 * 2 + 8 * 1) mod 11 = 0
+
+Which proves that the ISBN is valid.
+
+### Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `exercism/python/<exerciseName>` directory.
+
+For example, if you're submitting `bob.py` for the Bob exercise, the submit command would be something like `exercism submit <path_to_exercism_dir>/python/bob/bob.py`.
+
+
+For more detailed information about running tests, code style and linting,
+please see the [help page](http://exercism.io/languages/python).
+
+## Source
+
+Converting a string into a number and some basic processing utilizing a relatable real world example. [https://en.wikipedia.org/wiki/International_Standard_Book_Number#ISBN-10_check_digit_calculation](https://en.wikipedia.org/wiki/International_Standard_Book_Number)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/isbn-verifier/exemple.py

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+def verify(isbn):
+    clear_isbn = remove_non_alphanumeric(isbn)
+    if len(clear_isbn) != 10:
+        return False
+
+    isbn_main_part = get_isbn_main_part(clear_isbn)
+    if not isbn_main_part.isdigit():
+        return False
+
+    check_digit = get_isbn_check_digit(clear_isbn)
+    if not check_digit.isdigit() and check_digit.upper() != 'X':
+        return False
+
+    if calculate_isbn_check_digit(isbn_main_part) != check_digit:
+        return False
+
+    return True
+
+
+def remove_non_alphanumeric(value):
+    return ''.join([x for x in str(value) if x.isalnum()])
+
+
+def get_isbn_main_part(isbn_value):
+    return isbn_value[:-1]
+
+
+def get_isbn_check_digit(isbn_value):
+    return isbn_value[-1:]
+
+
+def calculate_isbn_check_digit(isbn):
+    check_digit = 11 - (int(isbn[0:1]) * 10 +
+                        int(isbn[1:2]) * 9 +
+                        int(isbn[2:3]) * 8 +
+                        int(isbn[3:4]) * 7 +
+                        int(isbn[4:5]) * 6 +
+                        int(isbn[5:6]) * 5 +
+                        int(isbn[6:7]) * 4 +
+                        int(isbn[7:8]) * 3 +
+                        int(isbn[8:9]) * 2) % 11
+
+    if check_digit == 10:
+        return 'X'
+
+    return str(check_digit)

exercises/isbn-verifier/isbn_verifier.py

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+def verify(isbn):
+    pass

exercises/isbn-verifier/isbn_verifier_test.py

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+import unittest
+
+from isbn_verifier import verify
+
+
+# Tests adapted from `problem-specifications//canonical-data.json` @ v1.0.0
+
+class IsbnVerifierTests(unittest.TestCase):
+
+    def test_valid_isbn(self):
+        self.assertIs(verify('3-598-21508-8'), True)
+
+    def test_invalid_check_digit(self):
+        self.assertIs(verify('3-598-21508-9'), False)
+
+    def test_valid_with_X_check_digit(self):
+        self.assertIs(verify('3-598-21507-X'), True)
+
+    def test_invalid_check_digit_other_than_X(self):
+        self.assertIs(verify('3-598-21507-A'), False)
+
+    def test_invalid_character_in_isbn(self):
+        self.assertIs(verify('3-598-2K507-0'), False)
+
+    def test_invalid_X_other_than_check_digit(self):
+        self.assertIs(verify('3-598-2X507-0'), False)
+
+    def test_valid_isbn_without_separating_dashes(self):
+        self.assertIs(verify('3598215088'), True)
+
+    def test_valid_isbn_without_separating_dashes_with_X_check_digit(self):
+        self.assertIs(verify('359821507X'), True)
+
+    def test_invalid_isbn_without_check_digit_and_dashes(self):
+        self.assertIs(verify('359821507'), False)
+
+    def test_invalid_too_long_isbn_with_no_dashes(self):
+        self.assertIs(verify('3598215078X'), False)
+
+    def test_invalid_isbn_without_check_digit(self):
+        self.assertIs(verify('3-598-21507'), False)
+
+    def test_invalid_too_long_isbn(self):
+        self.assertIs(verify('3-598-21507-XA'), False)
+
+    def test_invalid_check_digit_X_used_for_0(self):
+        self.assertIs(verify('3-598-21515-X'), False)
+
+
+if __name__ == '__main__':
+    unittest.main()