How to Use a Dispatch Table in Python (Map Strings to Functions)

Maps string command names to callable functions in a dictionary, then dispatches calls safely with error handling.

Easy Python 3.9+ Aug 9, 2026 Functions & basics 14 views 0 copies

dispatch-table dictionary functions callbacks design-pattern

Python code

36 lines

Python 3.9+

def add(a, b):
    return a + b


def subtract(a, b):
    return a - b


def multiply(a, b):
    return a * b


def divide(a, b):
    if b == 0:
        raise ValueError("Division by zero")
    return a / b


dispatch = {
    "add": add,
    "subtract": subtract,
    "multiply": multiply,
    "divide": divide,
}


def apply_operation(operation, x, y):
    func = dispatch.get(operation)
    if func is None:
        raise KeyError(f"Unknown operation: {operation}")
    return func(x, y)


if __name__ == "__main__":
    result = apply_operation("multiply", 6, 7)
    print(result)

Output

stdout

How it works

The dispatch dictionary stores function references as values, keyed by string names. apply_operation looks up the function with dict.get(), which returns None for missing keys instead of raising a KeyError — then the explicit check converts that into a clear error message. Each function is called with the provided arguments, and the result is returned directly. This pattern avoids long chains of if/elif statements when mapping names to behaviors. The raise statements inside functions and the dispatcher give clear feedback for invalid input.

Common mistakes

Forgetting the `.get()` method and causing an unhelpful `KeyError` for unknown operations
Storing function calls (with parentheses) instead of function references in the dispatch dict
Not validating `None` results from `dict.get()` before attempting to call the function

Variations

Use `functools.partial` to bind extra arguments to each function in the dispatch table
Use a `match` statement (Python 3.10+) instead of a dict for imperative dispatch logic

Real-world use cases

A CLI tool that maps subcommand strings to their handler functions (e.g., `add`, `delete`, `status`).
An HTTP API router that maps endpoint names to view functions in a lightweight web framework.
An event-processing worker that dispatches named event types to the right handler callback.

How to Use a Dispatch Table in Python (Map Strings to Functions)

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Functions & basics

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