use a mapping

Use a mapping where appropriate, rather than a giant if or case statement.

I continue to see this again and again in production code, in many languages. Often we’re dealing with Enum and a more complex task than spelling numbers.

    def _convert(a):
        if a == 1:
            return 'one'
        elif a == 2:
        ...
        elif a == 10:
            return 'ten'
        else raise ValueError(f'unknown input: {a}')

Or worse, no helper, and each return is a result = assignment.

There’s no need for such code. Take advantage of map datastructures. They’re fast! And concise. Fewer places for a one-off code change to creep into the middle of it.

    num_to_str = {
        1: 'one',
        2: 'two',
        ...
        10: 'ten',
    }
    def _convert(a):
        return num_to_str[a]

That’s a str -valued mapping, but we could manipulate functions or classes just as easily. Leave out the usual () parentheses, so we have the function rather than its evaluation.

    { '+': sum, '*': prod }

    {
        'too big': OverflowError,
        'no file': FileNotFoundError,
        'CTRL/C': InterruptedError,
    }

(Image credit: torisan3500 )

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