Python is one of my favorite programming languages. It’s simple and versatile. There’s a reason it’s so popular. It’s fun to use, and you can get a lot of work done without writing a ton of code. - me, a bunch of times “I’ll just write a quick Python script for this” One of the things Python does well is abstracting complexity. One example of that is the Python function. A function is a reusable set of instructions to perform a task. Functions aren’t unique to Python; they work mostly the same as in other languages. If you want to know how to write and call a function in , here’s a step-by-step guide. Python The Anatomy of a Python Function Before you can call a function, you have to write a function. Thankfully, that’s easy. Let’s look at the main components of a function. def function_name(parameters):
    # Your code goes here
    return The keyword ‘def’ refers to a followed by your chosen function name and parentheses enclosing optional parameters. Parameters are anything you want to put into the function. function definition The action happens in the (Where it says your code goes here). This is where we put statements that make the function do work. function body The keyword allows you to send data of the function. Note: You don’t always need to return a value. It’s optional. return out So the main parts are: definition (def keyword) function name parameters body (what the function does) return value All of these, put together, form a function. Calling a Python Function Once we’ve defined a function, calling it is as straightforward as writing the function’s name followed by parentheses. If our function requires , we place these inside the parentheses. These are optional. parameters Let’s build a simple function to display whenever we call it. Hello World def hello_world():
    print("Hello, World!") Even though there are no parameters or a return value, this is a function in Python. The “output” of the function is printing Hello World. We can call this function with this line of code: hello_world() And this will output “Hello, World!” to your console whenever we call it. In fact, if we call it five times: hello_world()
hello_world()
hello_world()
hello_world()
hello_world() It will display the same thing five times. Congratulations! You’ve just written your first function in Python. The Power of Function Parameters in Python Parameters are pieces of data we the function. The work of the function depends on what we pass into it. Parameters enable us to make our Python functions dynamic and reusable. We can define a function that takes parameters, allowing us to pass different arguments each time we call the function. pass into def greet(name):
    print("Hello, " + name + "!")

greet("Jeremy")
greet("Susie")
greet("Jim") Here, the function takes one parameter, ‘name.’ When we call the function, we can pass any name we wish to greet. greet() Dealing with Multiple Parameters Python functions can accept multiple parameters, allowing us to add dynamic inputs to our function calls. def greet(name, city):
    print("Hello, " + name + " from " + city + "!")

greet("Jeremy", "Gaston")
greet("Susie", "Forest Grove")
greet("Jim", "Cornelius") Now takes two parameters, ‘name’ and ‘city’. greet() And it’s that easy. Congrats! You can now pass data into a . function in Python Leveraging Default Parameters in Python Functions Sometimes, you want to set a value for a parameter as a default. This allows the function to be called even if no data was passed. Rather than throwing an error, it will populate the value with anything you specify. def greet(name="User"):
    print("Hello, " + name + "!")

greet()
greet("Alice") Here, ‘greet()’ function has a default parameter ‘name’ set to ‘User’. If no argument is passed, the function greets ‘User.’ If we provide a name, it greets that name instead. It’s a good way to set defaults. Python Return Statement The ‘return’ statement exits a function and returns a value. With it, we can store the output of a function in a variable for future use. def square(number):
    return number * number

result = square(5)
print(result) In this case, function returns the square of the input number. The output can be stored in a variable and used later. square() The return keyword is used to push values out of the function to use in your program. Functions are awesome! Python functions are a powerful tool in a programmer’s arsenal. They encapsulate code blocks for specific tasks, enhancing the readability and maintainability of the code. Understanding how to call a function in Python, employ parameters, and leverage the ‘return’ statement is fundamental to proficient Python programming. Remember, practice is key! The more you use this, the more second nature it will become for you. The Versatility of Variable Arguments in Python Python introduces an interesting feature in functions: variable-length arguments. Sometimes, we don’t know how many arguments will be passed to a function. Python’s variable arguments (*args and **kwargs) solve this problem. def add_numbers(*args):
    return sum(args)

print(add_numbers(3, 5, 7, 9)) In the example uses to accept any number of parameters. The function then sums up all the numbers and returns the total. add_numbers() *args In-Depth with Python Keyword Arguments Python functions also allow , which enable us to identify arguments by name. This can be extremely handy when a function has many parameters, and it improves the readability of our code. keyword arguments def describe_pet(pet_name, animal_type='dog'):
    print("I have a " + animal_type + ".")
    print("My " + animal_type + "'s name is " + pet_name + ".")

describe_pet(pet_name='Willie') In this scenario, ‘describe_pet()’ is called with the ‘pet_name’ keyword argument. The function also includes a default argument, , set to . animal_type dog Grasping Anonymous Functions in Python: Lambda Python’s ‘lambda’ function is a small, anonymous function defined with the ‘lambda’ keyword rather than ‘def.’ Lambda functions can accept any number of arguments but only have one expression. multiply = lambda x, y: x * y

print(multiply(5, 4)) In the code above, a lambda function is defined to multiply two numbers, and it’s called with two arguments: 5 and 4. The function returns the result of the multiplication. Conclusion Congratulations! You now know how to work with functions in Python. We have covered: The main parts of a function Calling a Python function Using function parameters Using multiple parameters Creating default parameters Returning data with the return statement Using variable parameters Leveraging lambda functions Functions in Python provide a way of organizing and reusing code to create cleaner programming solutions. As a next step, we recommend you delve deeper into advanced Python function topics such as recursive functions, decorators, and generator functions. I’ll be adding more content like this to Hackernoon very soon. and come back for more cool . Follow me Python tutorials Also published . here

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