Writing Your Own Functions
Package code into reusable, named pieces with def.
A function is a named block of code that you can run whenever you need it. You have already used built-in functions like print() and len(). Now you will write your own with the def keyword.
Python
def greet():
print("Welcome to GateShala!")
greet()
greet()Output
Welcome to GateShala! Welcome to GateShala!
Parameters and return values
Values passed into a function are called arguments; the names that receive them are parameters. The return statement sends a result back to whoever called the function.
Python
def area_of_rectangle(width, height):
return width * height
room = area_of_rectangle(4, 3)
print("Room area:", room)
print("Table area:", area_of_rectangle(1.5, 0.8))Output
Room area: 12 Table area: 1.2000000000000002
Default and keyword arguments
A parameter can have a default value, which is used when the caller leaves it out. Callers can also name arguments, which makes the call easier to read.
Python
def make_tea(cups, sugar=1, milk=True):
kind = "milk tea" if milk else "black tea"
return f"{cups} cup(s) of {kind} with {sugar} spoon(s) of sugar"
print(make_tea(2))
print(make_tea(1, sugar=0, milk=False))Output
2 cup(s) of milk tea with 1 spoon(s) of sugar 1 cup(s) of black tea with 0 spoon(s) of sugar
Why use functions?
- Reuse: write the logic once and call it many times.
- Readability: a good name like
area_of_rectangleexplains what the code does. - Testing: small functions are easy to check one at a time.