Functions

Define, call, and return values from functions so you can reuse clear pieces of code.

10 min read 10 quiz questions

Your first function

A function is a named, reusable piece of code. You define it once, then call it whenever you need it.

Use def to define a function. The indented lines are its body.

def function_name(parameter):
    # code to run
    return value

function_name(argument)

Example 1: Define and call a function

def greet(name):
    """Print a friendly greeting."""
    print(f"Hello, {name}!")

greet("Mina")

name is a parameter: a name in the function definition. "Mina" is an argument: the actual value you pass when calling the function.

The string under the definition is a docstring. It briefly tells readers what the function does.

Return a result

Example 2: Return a value

def add(left, right):
    return left + right

result = add(3, 4)
print(result)

return sends a value back to the code that called the function. Here, add(3, 4) produces 7, which is stored in result.

Returning multiple values

Example 3: Return multiple values

def split_full_name(full_name):
    """Return the first and last parts of a name."""
    first, last = full_name.split()
    return first, last

first_name, last_name = split_full_name("Ada Lovelace")
print(first_name)
print(last_name)

Key points

Define a function with def and a name.
Call a function with parentheses.
Parameters receive arguments passed to a call.
Use return to send a result back.
Docstrings explain what a function does.

Worked example

A grocery app converts taka to dollars in many places — write the conversion ONCE as a function and reuse it.

Example

def tk_to_usd(taka, rate=110):
    return round(taka / rate, 2)

print(tk_to_usd(550))
print(tk_to_usd(550, 100))

How it works, step by step

def names the function and lists its parameters.
return hands the result back to whoever called it.
rate=110 is a default: callers may omit it (first call) or override it (second call).

References & Further Reading

Related entries from PyLabs's own reference library.

callable() (Check whether an object can be called with parentheses.)
help() (Open Python's built-in help system for a topic.)

Your notes

Practice exercise

Not passed yet

Write a function named square that accepts one number and returns its square. Call it with 3 and print the result.

Expected output: 9

# Write your code below

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Functions quiz

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