Exercism v3 launches on Sept 1st 2021. Learn more! πππ

Published at Jul 13 2018
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Instructions

Test suite

Solution

Parse and evaluate simple math word problems returning the answer as an integer.

Add two numbers together.

What is 5 plus 13?

Evaluates to 18.

Handle large numbers and negative numbers.

Now, perform the other three operations.

What is 7 minus 5?

2

What is 6 multiplied by 4?

24

What is 25 divided by 5?

5

Handle a set of operations, in sequence.

Since these are verbal word problems, evaluate the expression from
left-to-right, *ignoring the typical order of operations.*

What is 5 plus 13 plus 6?

24

What is 3 plus 2 multiplied by 3?

15 (i.e. not 9)

If you'd like, handle exponentials.

What is 2 raised to the 5th power?

32

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 the appropriate command below (why they are different):

- Python 2.7:
`py.test wordy_test.py`

- Python 3.4+:
`pytest wordy_test.py`

Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
`python -m pytest wordy_test.py`

`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`

Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/wordy`

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 the help page.

Inspired by one of the generated questions in the Extreme Startup game. https://github.com/rchatley/extreme_startup

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

```
import unittest
from wordy import calculate
# Tests adapted from `problem-specifications//canonical-data.json` @ v1.1.0
class WordyTest(unittest.TestCase):
def test_addition(self):
self.assertEqual(calculate("What is 1 plus 1?"), 2)
def test_more_addition(self):
self.assertEqual(calculate("What is 53 plus 2?"), 55)
def test_addition_with_negative_numbers(self):
self.assertEqual(calculate("What is -1 plus -10?"), -11)
def test_large_addition(self):
self.assertEqual(calculate("What is 123 plus 45678?"), 45801)
def test_subtraction(self):
self.assertEqual(calculate("What is 4 minus -12?"), 16)
def test_multiplication(self):
self.assertEqual(calculate("What is -3 multiplied by 25?"), -75)
def test_division(self):
self.assertEqual(calculate("What is 33 divided by -3?"), -11)
def test_multiple_addition(self):
self.assertEqual(calculate("What is 1 plus 1 plus 1?"), 3)
def test_addition_then_subtraction(self):
self.assertEqual(calculate("What is 1 plus 5 minus -2?"), 8)
def test_multiple_subtraction(self):
self.assertEqual(calculate("What is 20 minus 4 minus 13?"), 3)
def test_subtraction_then_addition(self):
self.assertEqual(calculate("What is 17 minus 6 plus 3?"), 14)
def test_multiple_multiplication(self):
self.assertEqual(
calculate("What is 2 multiplied by -2 multiplied by 3?"), -12)
def test_addition_then_multiplication(self):
self.assertEqual(calculate("What is -3 plus 7 multiplied by -2?"), -8)
def test_multiple_division(self):
self.assertEqual(
calculate("What is -12 divided by 2 divided by -3?"), 2)
def test_unknown_operation(self):
with self.assertRaisesWithMessage(ValueError):
calculate("What is 52 cubed?")
def test_non_math_question(self):
with self.assertRaisesWithMessage(ValueError):
calculate("Who is the President of the United States?")
# Additional tests for this track
def test_missing_operation(self):
with self.assertRaisesWithMessage(ValueError):
calculate("What is 2 2 minus 3?")
def test_missing_number(self):
with self.assertRaisesWithMessage(ValueError):
calculate("What is 7 plus multiplied by -2?")
# Utility functions
def setUp(self):
try:
self.assertRaisesRegex
except AttributeError:
self.assertRaisesRegex = self.assertRaisesRegexp
def assertRaisesWithMessage(self, exception):
return self.assertRaisesRegex(exception, r".+")
if __name__ == '__main__':
unittest.main()
```

```
class Calculator:
OPERATORS = {"plus": "+",
"minus": "-",
"multiplied by": "*",
"divided by": "/",
"What is ": "",
"?": ""}
VALID_TOKENS = set(OPERATORS.values())
def __init__(self, inp):
self.inp = inp
self.tokenized = self.tokenize(inp)
self.tokens = self.tokenized.split(" ")
def calculate(self):
if not self.valid():
raise ValueError
operator_stack = self.operator_stack()
num_stack = self.num_stack()
while len(operator_stack) > 0:
operator = operator_stack.pop(0)
num1 = num_stack.pop(0)
num2 = num_stack.pop(0)
num_stack.insert(0, self.evaluate(operator, num1, num2))
return num_stack.pop(0)
def evaluate(self, operator, num1, num2):
return eval(str(num1) + operator + str(num2))
def num_stack(self):
return map(int, filter(self.digit, self.tokens))
def operator_stack(self):
return filter(self.operator, self.tokens)
def valid(self):
return (self.valid_elements() and
not self.consecutive_tokens() and
not self.consecutive_digits())
def consecutive_tokens(self):
return any(self.operator(i) and self.operator(j) for i, j in
self.slices_of_two())
def consecutive_digits(self):
return any(self.digit(i) and self.digit(j) for i, j in
self.slices_of_two())
def slices_of_two(self):
return zip(self.tokens, self.tokens[1:])
def valid_elements(self):
return all(self.valid_element(element) for element in self.tokens)
@classmethod
def valid_element(cls, element):
return element in cls.VALID_TOKENS or cls.digit(element)
@classmethod
def tokenize(cls, inp):
for operator, token in cls.OPERATORS.items():
inp = inp.replace(operator, token)
return inp
@staticmethod
def digit(element):
return element.lstrip("-").isdigit()
@classmethod
def operator(cls, element):
return element in cls.OPERATORS.values()
def calculate(inp):
return Calculator(inp).calculate()
```

A huge amount can be learned from reading other peopleβs code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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