Python Functions: A Beginners Guide
Introduction
A function is a block of code which only runs when it is called.
Python gives you many built-in functions like print(), etc. but you can also create your own functions. These functions are called user-defined functions
Creating a Function
Here are simple rules to define a function in Python:
- Function blocks begin with the keyword def followed by the function name and parentheses ( ( ) ).
- Any input parameters or arguments should be placed within these parentheses. You can also define parameters inside these parentheses.
- The first statement of a function can be an optional statement — the documentation string of the function or docstring.
- The code block within every function starts with a colon (:) and is indented.
- The statement return [expression] exits a function, optionally passing back an expression to the caller. A return statement with no arguments is the same as return None.
Example
The following function prints a string on the standard screen
Calling a Function
To call a function, use the function name followed by parenthesis
Function Arguments
Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma.
Example
The following example has a function with one argument (fname). When the function is called, we pass along a first name, which is used inside the function to print the full name
Number of Arguments
By default, a function must be called with the correct number of arguments. Meaning that if your function expects 2 arguments, you have to call the function with 2 arguments, not more, and not less.
If you try to call the function with 1 or 3 arguments, you will get an error.
This function expects 2 arguments, and gets 2 arguments:
Arbitrary Arguments, *args
If you do not know how many arguments that will be passed into your function, add a * before the parameter name in the function definition.
Keyword Arguments
You can also send arguments with the key = value syntax
Arbitrary Keyword Arguments, **kwargs
If you do not know how many keyword arguments that will be passed into your function, add two asterisk: ** before the parameter name in the function definition
Passing a List as an Argument
You can send any data types of argument to a function. If you send a List as an argument, it will still be a List when it reaches the function:
The return Statement
To let a function return a value, use the return statement
The pass Statement
function definitions cannot be empty, but if you for some reason have a function definition with no content, put in the pass statement to avoid getting an error
Recursion
Recursion is a common mathematical and programming concept. It means that a function calls itself. This has the benefit of meaning that you can loop through data to reach a result
Example
In this example, tri_recursion() is a function that we have defined to call itself (“recurse”). We use the k variable as the data, which decrements (-1) every time we recurse. The recursion ends when the condition is not greater than 0 (i.e. when it is 0).
Conclusion
I trust you find this guide on python functions useful, as always my advice is do lots of practice in order to master functions. Feel free to ask your questions in the comment section or reach out to me on twitter @AlphonseBrando2 . Cheers!
