Functions are reusable blocks of code that can be executed more than once in a program. You can access a function by its name. There are many built-in functions in Python like print(), len(), str(). You can define your own function using def keyword followed by the name of your function.
def my_function():
""" A simple function that only prints a text to console."""
print("> My function is executed")
Function Arguments
Sometimes functions need some arguments to work properly. For instance, consider you are coding a function that adds two numbers and prints the result. For this scenario, your function definition should take two arguments.
def print_sum(num1, num2):
""" This function adds two numbers. """
print("Sum of two numbers is: " + str(num1 + num2))
print_sum(3, 5)
# Output:
# Sum of two numbers is: 8
Arguments with Default Values
You can assign a default value to an argument. In the following example, the argument greeting_word has a default value “Hello”. If you provide a value for greeting_word argument when calling greet() function, provided value will be used instead of the default value.
def greet(name, greeting_word = "Hello"):
print(greeting_word + " " + name)
greet("John") # prints "Hello John"
greet("John", "Hi") # prints "Hi John"
Returning Values
Sometimes you might need functions that return a value. For instance, if you need to calculate the area of a circle you can write a function to keep your logic modular and reusable.
import math
def area_of_circle(r):
""" This function returns area of a circle """
a = r**2 * math.pi
return a
area = area_of_circle(1)
print("Area of a circle with radius 1 is: " + str(area))
# Area of a circle with radius 1 is: 3.14159...
Keyword Arguments
Normally, you give arguments to a function in the same order as function definition. For print_employee_info function, first argument is name, second argument is surname and third argument is id.
However, you can change the order if you specify the argument name as name-value pairs.
def print_employee_info(name, surname, id):
print("EmployeeInfo -> Name: " + name +
", Surname: " + surname + ", Id: " + str(id))
print_employee_info("George", "Miller", 5)
print_employee_info(surname = "Miller", id = 5, name = "George")
Arbitrary Number of Arguments
Some functions can take arbitrary number of arguments. These arguments are also called varargs (variable number of arguments). Syntax for a vararg is (*arg).
minimum function in the following example can take any number of arguments. The function iterates all arguments in a loop and returns the minimum value.
def minimum(*numbers):
min_number = numbers[0]
for number in numbers:
if number < min_number:
min_number = number
return min_number