PythonFunctions
Python Functions
A function is a block of code which only runs when it is called.
A function can return data as a result.
A function helps avoiding code repetition.
Creating a Function
In Python, a function is defined using thedef keyword, followed by a function name and parentheses:
Example
print("Hello from a function")
This creates a function namedmy_function that prints "Hello from a function" when called.
The code inside the function must be indented. Python uses indentation to define code blocks.
Calling a Function
To call a function, write its name followed by parentheses:
You can call the same function multiple times:
Example
print("Hello from a function")
my_function()
my_function()
my_function()
Function Names
Function names follow the same rules as variable names in Python:
- A function name must start with a letter or underscore
- A function name can only contain letters, numbers, and underscores
- Function names are case-sensitive (
myFunctionandmyfunctionare different)
Example
Valid function names:
_private_function()
myFunction2()
It's good practice to use descriptive names that explain what the function does.
Why Use Functions?
Imagine you need to convert temperatures from Fahrenheit to Celsius several times in your program. Without functions, you would have to write the same calculation code repeatedly:
Example
Without functions - repetitive code:
celsius1 = (temp1 - 32) * 5 / 9
print(celsius1)
temp2 = 95
celsius2 = (temp2 - 32) * 5 / 9
print(celsius2)
temp3 = 50
celsius3 = (temp3 - 32) * 5 / 9
print(celsius3)
With functions, you write the code once and reuse it:
Example
With functions - reusable code:
return (fahrenheit - 32) * 5 / 9
print(fahrenheit_to_celsius(77))
print(fahrenheit_to_celsius(95))
print(fahrenheit_to_celsius(50))
Return Values
Functions can send data back to the code that called them using thereturn statement.
When a function reaches areturn statement, it stops executing and sends the result back:
Example
A function that returns a value:
return "Hello from a function"
message = get_greeting()
print(message)
You can use the returned value directly:
Example
Using the return value directly:
return "Hello from a function"
print(get_greeting())
If a function doesn't have areturn statement, it returnsNone by default.
The pass Statement
Function definitions cannot be empty. If you need to create a function placeholder without any code, use thepass statement:
Thepass statement is often used when developing, allowing you to define the structure first and implement details later.
