1. What is this?
A function is a named block you can call. def greet(name): declares one with parameter name. The indented lines are its body. return sends a value back. Calling greet("Ava") runs the body with name = "Ava".
2. Why do we use it?
Reuse: one tested block, called with different inputs across your program.
3. Syntax breakdown
def greet(name):
def starts a function definition. name is the parameter.
return f"Hello, {name}"Body (indented). Builds and returns the greeting.
print(greet("Ava"))Calls the function, prints what it returned.
5. Common mistakes
- Forgetting the colon after def ...():.
- Forgetting return, so the call gives None.
- Calling with the wrong number of arguments.
Practice task
Write double(n) returning n * 2, then print(double(7)).
Hint
def double(n): on line 1, indented return on line 2.
Try it below — tests run automatically when you press Run.
python
Output
Press Run to see output.
Mini quiz
3 questions. Answer, then check.
1. What keyword starts a function?
2. What does return do?
3. What is the value of a call with no return?