Defining Functions

Defining a function

JavaScript:

function add(a, b) {
  return a + b;
}

Python:

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

Notice the pattern you already know from earlier phases:

Calling a function

Exactly the same as JS:

result = add(2, 3)
print(result)   # 5

Parameters

a and b above are parameters — the values a function expects when it's called. Python doesn't require declaring their type (we'll add that with type hints next), it just uses whatever value gets passed in.

return

return works exactly like in JS — it sends a value back to the caller and immediately exits the function.

def is_adult(age):
    if age >= 18:
        return True
    return False

print(is_adult(20))   # True

If a Python function has no return statement, it returns None — the same idea as a JS function with no return returning undefined.

def greet(name):
    print(f"Hello {name}")

result = greet("John")
print(result)   # None