006_Arithmetic_Formatter.md

This chanllenge is come from freecodecamp.org website. You can find it from here: https://www.freecodecamp.org/learn/scientific-computing-with-python/scientific-computing-with-python-projects/arithmetic-formatter

Assignment

Students in primary school often arrange arithmetic problems vertically to make them easier to solve. For example, "235 + 52" becomes:

  235
+  52
-----

Create a function that receives a list of strings that are arithmetic problems and returns the problems arranged vertically and side-by-side. The function should optionally take a second argument. When the second argument is set to True, the answers should be displayed.

For example

Function Call:

arithmetic_arranger(["32 + 698", "3801 - 2", "45 + 43", "123 + 49"])

Output:

   32      3801      45      123
+ 698    -    2    + 43    +  49
-----    ------    ----    -----

Function Call:

arithmetic_arranger(["32 + 8", "1 - 3801", "9999 + 9999", "523 - 49"], True)

Output:

  32         1      9999      523
+  8    - 3801    + 9999    -  49
----    ------    ------    -----
  40     -3800     19998      474

Rules

The function will return the correct conversion if the supplied problems are properly formatted, otherwise, it will return a string that describes an error that is meaningful to the user.

• Situations that will return an error:
  • If there are too many problems supplied to the function. The limit is five, anything more will return: Error: Too many problems.
  • The appropriate operators the function will accept are addition and subtraction. Multiplication and division will return an error. Other operators not mentioned in this bullet point will not need to be tested. The error returned will be: Error: Operator must be '+' or '-'.
  • Each number (operand) should only contain digits. Otherwise, the function will return: Error: Numbers must only contain digits.
  • Each operand (aka number on each side of the operator) has a max of four digits in width. Otherwise, the error string returned will be: Error: Numbers cannot be more than four digits.
• If the user supplied the correct format of problems, the conversion you return will follow these rules:
  • There should be a single space between the operator and the longest of the two operands, the operator will be on the same line as the second operand, both operands will be in the same order as provided (the first will be the top one and the second will be the bottom.
  • Numbers should be right-aligned.
  • There should be four spaces between each problem.
  • There should be dashes at the bottom of each problem. The dashes should run along the entire length of each problem individually. (The example above shows what this should look like.)

A reference code

def f(s):
    l = s.split(' ')
    try:
        a, op, b = int(l[0]), l[1], int(l[2])
    except ValueError:
        raise Exception('Error: Numbers must only contain digits.')
    if not (op == '+' or op == '-'):
        raise Exception('Error: Operator must be \'+\' or \'-\'.')
    if a > 9999 or b > 9999:
        raise Exception('Error: Numbers cannot be more than four digits.')
    c = eval(s)
    max_len = len(str(max(a, b))) + 2

    r = []
    r.append(str(a).rjust(max_len, ' '))
    r.append(op + ' ' + str(b).rjust(max_len - 2, ' '))
    r.append('-' * max_len)
    r.append(str(c).rjust(max_len, ' '))
    return r


def arithmetic_arranger(problems, show_result=False):
    if len(problems) > 5:
        return 'Error: Too many problems.'

    arranged_problems = ''
    d = []
    for problem in problems:
        try:
            ps = f(problem)
            d.append(ps)
        except Exception as e:
            return str(e)

    n = 3
    if show_result:
        n = 4

    for i in range(n):
        for j in range(len(d)):
            ps = d[j]
            if j == 0:
                arranged_problems = arranged_problems + ps[i]
            else:
                arranged_problems = arranged_problems + '    ' + ps[i]
        if i != n - 1:
            arranged_problems = arranged_problems + '\n'

    return arranged_problems

Here is the unit test code:

import unittest
from arithmetic_arranger import arithmetic_arranger


# the test case
class UnitTests(unittest.TestCase):
    def test_arrangement(self):
        actual = arithmetic_arranger(["3 + 855", "3801 - 2", "45 + 43", "123 + 49"])
        expected = "    3      3801      45      123\n+ 855    -    2    + 43    +  49\n-----    ------    ----    -----"
        self.assertEqual(actual, expected, 'Expected different output when calling "arithmetic_arranger()" with ["3 + 855", "3801 - 2", "45 + 43", "123 + 49"]')

        actual = arithmetic_arranger(["11 + 4", "3801 - 2999", "1 + 2", "123 + 49", "1 - 9380"])
        expected = "  11      3801      1      123         1\n+  4    - 2999    + 2    +  49    - 9380\n----    ------    ---    -----    ------"
        self.assertEqual(actual, expected, 'Expected different output when calling "arithmetic_arranger()" with ["11 + 4", "3801 - 2999", "1 + 2", "123 + 49", "1 - 9380"]')

    def test_too_many_problems(self):
        actual = arithmetic_arranger(["44 + 815", "909 - 2", "45 + 43", "123 + 49", "888 + 40", "653 + 87"])
        expected = "Error: Too many problems."
        self.assertEqual(actual, expected, 'Expected calling "arithmetic_arranger()" with more than five problems to return "Error: Too many problems."')

    def test_incorrect_operator(self):
        actual = arithmetic_arranger(["3 / 855", "3801 - 2", "45 + 43", "123 + 49"])
        expected = "Error: Operator must be '+' or '-'."
        self.assertEqual(actual, expected, '''Expected calling "arithmetic_arranger()" with a problem that uses the "/" operator to return "Error: Operator must be '+' or '-'."''')
        
    def test_too_many_digits(self):
        actual = arithmetic_arranger(["24 + 85215", "3801 - 2", "45 + 43", "123 + 49"])
        expected = "Error: Numbers cannot be more than four digits."
        self.assertEqual(actual, expected, 'Expected calling "arithmetic_arranger()" with a problem that has a number over 4 digits long to return "Error: Numbers cannot be more than four digits."')

    def test_only_digits(self):
        actual = arithmetic_arranger(["98 + 3g5", "3801 - 2", "45 + 43", "123 + 49"])
        expected = "Error: Numbers must only contain digits."
        self.assertEqual(actual, expected, 'Expected calling "arithmetic_arranger()" with a problem that contains a letter character in the number to return "Error: Numbers must only contain digits."')

    def test_solutions(self):
        actual = arithmetic_arranger(["32 - 698", "1 - 3801", "45 + 43", "123 + 49"], True)
        expected = "   32         1      45      123\n- 698    - 3801    + 43    +  49\n-----    ------    ----    -----\n -666     -3800      88      172"
        self.assertEqual(actual, expected, 'Expected solutions to be correctly displayed in output when calling "arithmetic_arranger()" with arithmetic problems and a second argument of `True`.')


if __name__ == "__main__":
    unittest.main()