A function is a named set of steps you can use again. You've used some already: print(), len(), int(). With def you make your own. The indented lines under def are the function's body; they don't run until the function is called.
def greet(name):
print("Hi, " + name)
greet("Ana")
greet("Sam")Hi, Ana Hi, Sam
The names in the brackets of def are parameters: when you call greet("Ana"), the parameter name holds "Ana" for that call. The value you pass in is called an argument.
return sends a value back to whoever called the function, and the function stops there. Printing and returning are different: a function that only prints shows something on screen, but you can't use its result in a sum. A function without a return gives back None.
def area(width, height):
return width * height
print(area(3, 4) + area(2, 5))22
Variables made inside a function belong to it (they're local) and disappear when it returns, so two functions can each have their own total without clashing. Small functions with clear names make a program much easier to read and to fix.
What does this print?
def double(n):
return n * 2
print(double(double(3)))| def name(params): | Defines a function. The body is indented. |
|---|---|
| return value | Sends the value back and ends the function. |
| name(args) | Calls the function. |
| None | What a function gives back when it has no return. |