add exercise

python/grains/.exercism/config.json

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+{
+  "blurb": "Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.",
+  "authors": [],
+  "contributors": [
+    "behrtam",
+    "BethanyG",
+    "cmccandless",
+    "denislooby",
+    "Dog",
+    "kytrinyx",
+    "lowks",
+    "MojitoMonday",
+    "N-Parsons",
+    "pheanex",
+    "sdublish",
+    "sjakobi",
+    "smalley",
+    "tqa236",
+    "yawpitch"
+  ],
+  "files": {
+    "solution": [
+      "grains.py"
+    ],
+    "test": [
+      "grains_test.py"
+    ],
+    "example": [
+      ".meta/example.py"
+    ]
+  },
+  "source": "JavaRanch Cattle Drive, exercise 6",
+  "source_url": "http://www.javaranch.com/grains.jsp"
+}

python/grains/.exercism/metadata.json

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+{"track":"python","exercise":"grains","id":"f9029e1bd44842f7b92e33ad000b6e46","url":"https://exercism.org/tracks/python/exercises/grains","handle":"Nebucatnetzer","is_requester":true,"auto_approve":false}

python/grains/HELP.md

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+# Help
+
+## Running the tests
+
+To run the included *tests*, run the test file using the `pytest` module, replacing `{exercise_name}`:
+
+```bash
+$ python3 -m pytest {exercise_name}_test.py
+```
+
+Many IDE's and code editors have built-in support for using Pytest to run tests; check them out [here](https://github.com/exercism/python/blob/main/docs/TOOLS.md#editors-and-ides).
+
+For more information about running tests using `pytest`, checkout our [Python testing guide](https://github.com/exercism/python/blob/main/docs/TESTS.md#pytest).
+
+### 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 `python3 -m pytest -h`.
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit grains.py` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Python track's documentation](https://exercism.org/docs/tracks/python)
+- [Exercism's support channel on gitter](https://gitter.im/exercism/support)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+Below are some resources for getting help if you run into trouble:
+
+- [The PSF](https://www.python.org) hosts Python downloads, documentation, and community resources.
+- [Python Community on Discord](https://pythondiscord.com/) is a very helpful and active community.
+- [#python on Libera.chat](https://www.python.org/community/irc/) this is where the cored developers for the language hang out and get work done.
+- [Exercism on Gitter](https://gitter.im/exercism/home) join the Python room for Python-related questions or problems.
+- [/r/learnpython/](https://www.reddit.com/r/learnpython/) is a subreddit designed for Python learners.
+- [Python Community Forums](https://discuss.python.org/)
+- [Pythontutor](http://pythontutor.com/) for stepping through small code snippets visually.
+
+
+Additionally, [StackOverflow](http://stackoverflow.com/questions/tagged/python) is a good spot to search for your problem/question to see if it has been answered already.
+ If not - you can always [ask](https://stackoverflow.com/help/how-to-ask) or [answer](https://stackoverflow.com/help/how-to-answer) someone else's question.

python/grains/README.md

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+# Grains
+
+Welcome to Grains on Exercism's Python Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Calculate the number of grains of wheat on a chessboard given that the number
+on each square doubles.
+
+There once was a wise servant who saved the life of a prince. The king
+promised to pay whatever the servant could dream up. Knowing that the
+king loved chess, the servant told the king he would like to have grains
+of wheat. One grain on the first square of a chess board, with the number
+of grains doubling on each successive square.
+
+There are 64 squares on a chessboard (where square 1 has one grain, square 2 has two grains, and so on).
+
+Write code that shows:
+- how many grains were on a given square, and
+- the total number of grains on the chessboard
+
+## For bonus points
+
+Did you get the tests passing and the code clean? If you want to, these
+are some additional things you could try:
+
+- Optimize for speed.
+- Optimize for readability.
+
+Then please share your thoughts in a comment on the submission. Did this
+experiment make the code better? Worse? Did you learn anything from it?
+
+## Exception messages
+
+Sometimes it is necessary to [raise an exception](https://docs.python.org/3/tutorial/errors.html#raising-exceptions). When you do this, you should always 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. For situations where you know that the error source will be a certain type, you can choose to raise one of the [built in error types](https://docs.python.org/3/library/exceptions.html#base-classes), but should still include a meaningful message.
+
+This particular exercise requires that you use the [raise statement](https://docs.python.org/3/reference/simple_stmts.html#the-raise-statement) to "throw" a `ValueError` when the square input is out of range. The tests will only pass if you both `raise` the `exception` and include a message with it.
+
+To raise a `ValueError` with a message, write the message as an argument to the `exception` type:
+
+```python
+# when the square value is not in the acceptable range        
+raise ValueError("square must be between 1 and 64")
+```
+
+## Source
+
+### Contributed to by
+
+- @behrtam
+- @BethanyG
+- @cmccandless
+- @denislooby
+- @Dog
+- @kytrinyx
+- @lowks
+- @MojitoMonday
+- @N-Parsons
+- @pheanex
+- @sdublish
+- @sjakobi
+- @smalley
+- @tqa236
+- @yawpitch
+
+### Based on
+
+JavaRanch Cattle Drive, exercise 6 - http://www.javaranch.com/grains.jsp

python/grains/grains.py

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+def square(number):
+    if number <= 0 or number > 64:
+        raise ValueError("square must be between 1 and 64")
+    return 2 ** (number - 1)
+
+
+def total():
+    return 2 ** 64 - 1

python/grains/grains_test.py

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+import unittest
+
+from grains import (
+    square,
+    total,
+)
+
+# Tests adapted from `problem-specifications//canonical-data.json`
+
+
+class GrainsTest(unittest.TestCase):
+    def test_grains_on_square_1(self):
+        self.assertEqual(square(1), 1)
+
+    def test_grains_on_square_2(self):
+        self.assertEqual(square(2), 2)
+
+    def test_grains_on_square_3(self):
+        self.assertEqual(square(3), 4)
+
+    def test_grains_on_square_4(self):
+        self.assertEqual(square(4), 8)
+
+    def test_grains_on_square_16(self):
+        self.assertEqual(square(16), 32768)
+
+    def test_grains_on_square_32(self):
+        self.assertEqual(square(32), 2147483648)
+
+    def test_grains_on_square_64(self):
+        self.assertEqual(square(64), 9223372036854775808)
+
+    def test_square_0_raises_an_exception(self):
+        with self.assertRaises(ValueError) as err:
+            square(0)
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "square must be between 1 and 64")
+
+    def test_negative_square_raises_an_exception(self):
+        with self.assertRaises(ValueError) as err:
+            square(-1)
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "square must be between 1 and 64")
+
+    def test_square_greater_than_64_raises_an_exception(self):
+        with self.assertRaises(ValueError) as err:
+            square(65)
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "square must be between 1 and 64")
+
+    def test_returns_the_total_number_of_grains_on_the_board(self):
+        self.assertEqual(total(), 18446744073709551615)