Operation Dispatch Table

Medium ⏱ 12 min 50% acceptance ★★★★☆ 4.3

Write a small calculator library made of four functions add(a, b), subtract(a, b), multiply(a, b), divide(a, b), plus a function calculate(op, a, b) that looks up op (one of the strings "add", "subtract", "multiply", "divide") in a dict mapping operation names to functions and calls the matching function with a and b. If op is not a recognized key, return the string "Unknown operation".

Examples

Example 1

Input

calculate("multiply", 4, 5)

Output

Explanation

Looks up multiply in the dispatch table and calls multiply(4, 5).

Example 2

Input

calculate("modulo", 4, 5)

Output

Unknown operation

Explanation

modulo is not a key in the dispatch table.

Constraints

divide(a, b) may assume b != 0 for the given test cases.
The dispatch table must be built from the four named functions, not from if/elif chains.

Topics

Functionsfunctions in a dict

Companies

Deutsche BankGoldman SachsJPMorgan Chase

Hints

Hint 1

Build a dict like {"add": add, "subtract": subtract, ...} — function names without parentheses are references to the functions themselves.

Hint 2

Use dict.get(op) to look up safely, then check whether the result is None.

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