As your programs grow, you’ll find yourself writing the same steps again and again. A function lets you name a block of code once and then run it whenever you like, just by calling its name. You define one with the def keyword:
def say_hello():
print('Hello World')
say_hello()Hello World
Functions become far more useful when you feed them data. The values you pass in are called arguments; inside the function they become parameters you can use by name.
def greet(name):
print(f'Hello {name}')
greet('Alice')Hello Alice
Printing shows a value on screen; returning hands it back to the caller so the rest of your program can use it. The return statement does exactly that.
def add(a, b):
return a + b
result = add(5, 3)
print(result)8
The execution of a function introduces a new symbol table used for the local variables.
def scope_test():
x = 10
print(x)
scope_test()10
A function executes its code as soon as it is defined. Defining a function only creates it. The code inside does not run until the function is called.
Variables created inside a function can be accessed outside of it. Variables defined inside a function are local to that function and disappear when the function finishes.
A function must always have a return statement. If a function doesn’t have a return statement, it implicitly returns None.
() both when defining and calling.Watch how function calls, arguments, and local variables are managed in memory:
def square(num):
result = num * num
return result
val = square(4)What keyword is used to define a function in Python?
def — The def keyword is used to introduce a function definition.
If a function does not have a return statement, what does it return?
None — If a function doesn't have a return statement, it implicitly returns None.
Where are variables that are assigned inside a function stored?
In a local symbol table — Variables assigned inside a function are local to that function's execution.
Write a function called `multiply` that takes two parameters, multiplies them together, and returns the result. Then call it with 4 and 5 and print the result.
Use the def keyword, and remember to return a * b.
def multiply(a, b):
return a * b
print(multiply(4, 5))Create a function `say_goodbye` that takes a `name` parameter and prints 'Goodbye ' followed by the name. Call it with 'Bob'.
Use an f-string to easily insert the name parameter into the printed string.
def say_goodbye(name):
print(f'Goodbye {name}')
say_goodbye('Bob')