Python - 数学 - 数を扱う - 分数電卓(fractionsモジュール、Fraction、input関数、例外処理、TypeError)

Pythonからはじめる数学入門
原著

開発環境

• macOS High Sierra - Apple
• Emacs (Text Editor)
• Python 3.6 (プログラミング言語)

Pythonからはじめる数学入門 (Amit Saha (著)、黒川 利明 (翻訳)、オライリージャパン)の1章(数を扱う)、1.7(プログラミングチャレンジ)、問題1-4(分数電卓)を取り組んでみる。

コード(Emacs)

Python 3

#!/usr/bin/env python3
from fractions import Fraction


def add(a, b):
    print(f'Result of Addition: {a + b}')


def sub(a, b):
    print(f'Result of Subtraction: {a - b}')


def mul(a, b):
    print(f'Result of Multiplication: {a * b}')


def div(a, b):
    print(f'Result of Division({a} ÷ {b}): {a / b}')


ops = {'Add': add, 'Subtract': sub, 'Divide': div, 'Multiply': mul}

if __name__ == '__main__':
    while True:
        try:
            a = input('Enter first fraction: ')
            if a == 'q':
                break
            a = Fraction(a)
            b = Fraction(input('Enter second fraction: '))
            op = input(
                'Operation to perform - Add, Subtract, Divide, Multiply: ')
            op0 = ops.get(op)
            if op0:
                op0(a, b)
            else:
                print(f'Invalid operation: {op}')
        except TypeError as err:
            print(type(err), err)
        except Exception as err:
            print(type(err), err)

入出力結果(Terminal, Jupyter(IPython))

$ ./sample4.py
Enter first fraction: 3/4
Enter second fraction: 1/4
Operation to perform - Add, Subtract, Divide, Multiply: Add
Result of Addition: 1
Enter first fraction: 3/4
Enter second fraction: 1/4
Operation to perform - Add, Subtract, Divide, Multiply: Subtract
Result of Subtraction: 1/2
Enter first fraction: 3/4
Enter second fraction: 1/4
Operation to perform - Add, Subtract, Divide, Multiply: Divide
Result of Division(3/4 ÷ 1/4): 3
Enter first fraction: 3/4
Enter second fraction: 1/4
Operation to perform - Add, Subtract, Divide, Multiply: Multiply
Result of Multiplication: 3/16
Enter first fraction: -1.2
Enter second fraction: 3.4
Operation to perform - Add, Subtract, Divide, Multiply: Divide
Result of Division(-6/5 ÷ 17/5): -6/17
Enter first fraction: 1.2
Enter second fraction: -3.4
Operation to perform - Add, Subtract, Divide, Multiply: Divide
Result of Division(6/5 ÷ -17/5): -6/17
Enter first fraction: 1.2
Enter second fraction: 3.4
Operation to perform - Add, Subtract, Divide, Multiply: a
Invalid operation: a
Enter first fraction: 1.2
Enter second fraction: a
<class 'ValueError'> Invalid literal for Fraction: 'a'
Enter first fraction: q
$