A function can be called anywhere after the function has been declared. By itself, a function does nothing. But, when you need to use a function, you can call it, and the code within the function will be executed. In Python, there are two types of functions: user-defined and built-in.
Built-in functions are functions like:. User-defined functions are reusable blocks of code written by you, the developer. These blocks of code allow you to organize your code more efficiently. This is important because the more organized your code is, the easier it will be to maintain. Get matched to a bootcamp today.
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Defining a function refers to creating the function. This involves writing a block of code that we can call by referencing the name of our function. A function is denoted by the def keyword, followed by a function name, and a set of parenthesis. To do so, we can use this code:.
When we run our code, nothing happens. This is because, in order for our function to run, we need to call it. To do so, we can reference our function name like so:. Now, our functions can get as complex as we want them to be. Suppose we want to write a program that tells a user how many letters are in their name.
We could do so using this code:. In our first examples, we used empty parenthesis with our functions. This means that our functions did not accept any arguments. Arguments allow you to pass information into a function that the function can read. The parameter names in the function that our code accepts are: number1 and number2.
We define these between brackets which is where the parameter list is defined. Then, we print a statement to the console with the full mathematical sum written out, followed by the answer to the math problem.
We have specified required arguments. This is because we have set no default value for each argument. We must specify a number of arguments equal to those in the parameter list otherwise the Python interpreter will return an error. First, we specify the arguments 5 and Our program multiplies these values together to calculate Next, we specify the arguments 15 and 2, which our program multiplies. Two months after graduating, I found my dream job that aligned with my values and goals in life!
By default, the order of the arguments you pass in a function is the order in which they are processed by your program. For more information on arguments, check out our Python optional arguments tutorial. The terms parameter and argument refer to the same thing: passing information to a function.
But, there is a subtle difference between the two. A parameter is the variable inside the parenthesis in a function. In addition, understanding how Python functions work will help when working with a framework like Django or Flask which are both written in the Python programming language.
In fact, this is probably one of the key benefits, since you will be able to scan source files and look at various function definitions to understand what the software offers you. Recall that in general terms and regardless of the programming language, a function serves the purpose of reducing code duplication, breaking down larger problems into smaller ones, increasing the readability of software, boosting code reuse, and information hiding. Indeed the idea of functions as first-class citizens is popular in the JavaScript world.
What we mean when we say the first-class citizens is that functions are on the same level so to speak as other objects in the language.
As a result of this, you can assign functions to variables or even pass them as an argument to other functions. Just like in JavaScript, this helps to allow one to bend the language to their will. Just like PHP has many functions that ship as part of the language, so too does Python.
These are the built-in functions and include functions such as abs , dir , bin , len , and many more. If you want to create your own function, you can do so by making use of the def keyword, and we will take a look at this next.
The best way to learn is by doing. Therefore, let us try to create our very own function in Python and learn about what makes one, well, function. We got carried away there — I guess Adele has quite the far-reaching influence these days. In any event, we can see just how we constructed this first function.
Note that we start the function definition with the def keyword. If you even opened up a. It is for defining your functions. Right after the def keyword, we assign a name to identify the function followed by opening and closing parenthesis just like you might find in another programming language. After this, we find the colon : character. This indicates the beginning of the function code block which will house the logic that will get executed when a call is made to this function at a later time.
The next few lines look simple, but they are important! In Python Whitespace means something! Before each call to print there is exactly four blank whitespaces. If you get your whitespace wrong in Python, the compiler will throw an error. This is a bit of a controversial aspect of Python, but if you want to program in this language — you will need to get used to it. After we define the function, we make a call to it by simply typing hello on its own line with no spaces.
We can see from the output, that we may have a future in the music business. This function works just as we expect it might. Notice that in the definition of the function, we make an allowance for two parameters. These represent the two numbers we will pass to our function that it will add together. The program output shows us that it is working like a charm. In running this iteration of the adding function, we can see from the program output that the user was prompted for the numbers to add.
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 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. By default, parameters have a positional behavior and you need to inform them in the same order that they were defined.
Defining a function only gives it a name, specifies the parameters that are to be included in the function and structures the blocks of code. Once the basic structure of a function is finalized, you can execute it by calling it from another function or directly from the Python prompt. All parameters arguments in the Python language are passed by reference. It means if you change what a parameter refers to within a function, the change also reflects back in the calling function.
Here, we are maintaining reference of the passed object and appending values in the same object. There is one more example where argument is being passed by reference and the reference is being overwritten inside the called function. The parameter mylist is local to the function changeme.
Changing mylist within the function does not affect mylist. Required arguments are the arguments passed to a function in correct positional order. Here, the number of arguments in the function call should match exactly with the function definition. Keyword arguments are related to the function calls.
When you use keyword arguments in a function call, the caller identifies the arguments by the parameter name.
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