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Functions

15. Functions#

The purpose of Functions is grouping the code into organised, readable and reusable format. By using the functions, code redundancy can be reduced.

A soft rule of functions is that, an function should be Small and Do One Thing mentioned in Clean Code by Robert C. Martin.

Functions are nothing new to us. We have already used print function in our previous lessons, just that it is a built-in function. There are other built-in functions like help, len, sorted, map, filter, reduce etc…

In Python functions are created by using the keyword def followed by the function name and if required parameters.

def function_name(parameters):
    # statements...
    ...
    ...
    ...

Here function_name is the identifier for the function through which it can be called. parameters are optional in the function signature. A function may have any number of parameters to be bound to the function. As we already know we do use Indentation to group the statements, all the statements belonging to the function are indented in the function.

By convention function names should be in camelcase 🐪 and be a verb.

Let’s get started with a basic function

15.1. Simple function#

def greet():
    print("Hello Pythoneer! 😎")

greet()  # Calling the function

Hello Pythoneer! 😎

This is a pretty basic function which just prints to the console saying “Hello Pythoneer!😎”, as we are not returning anything using the return keyword, our function greet implicitly returns None object.

We could return objects from the function using the keyword return

def greet():
    return "Hello Pythoneer! 😎"

greet_word = greet()
print(greet_word)

Hello Pythoneer! 😎

15.2. Functions - First Class Objects#

In Python 🐍, Functions are First class objects. There are a few criteria defined for an object to be First class object like functions can be passed as argument, assigned to a variable, return a function.

15.2.1. Passing the function to a different function#

def first_function():
    print("One Pint of 🍺")

def second_function(func):
    func()
    print("Two Pints of beer 🍺🍺")

second_function(first_function)

One Pint of 🍺
Two Pints of beer 🍺🍺

Yippeee! We have successfully passed our first_function to the second_function where first_function is being called inside the second_function

15.2.2. Assigning the function to a variable#

# note that we are not calling the function, we are just assigning,
# if we call the function, the returned value would be assigned to our variable.
i_am_a_variable = first_function

i_am_a_variable()

One Pint of 🍺

15.2.3. Returning a function#

def lets_return_a_function():
    return first_function

obj = lets_return_a_function()
print(f"obj is {obj}")
print(f"obj name is {obj.__name__}")
print(f"Is obj callable? {callable(obj)}")

obj is <function first_function at 0x7e62ddae4fe0>
obj name is first_function
Is obj callable? True

Cheers again 🍻! We accomplished mission of returning the function. In the above example, we are printing the the obj itself which provides the __str__ representation of the obj, next we are printing the name of the obj which is the function name itself, and finally we are checking if our obj is callable, if an object is callable, then callable function returns True else False

15.2.4. Deletion of function object#

As we already know that everything in Python is an object, even function as well is an object. We can even delete our function using the del keyword.

del first_function
first_function()

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Cell In[12], line 2
      1 del first_function
----> 2 first_function()

NameError: name 'first_function' is not defined

As we deleted the first_function, if we try to call that function, we do get to see NameError saying first_function is not defined.

15.3. Types of Arguments#

As we already know we can pass the parameters to the function, we can give a try on those too.. But before trying out, let’s know about the types of Arguments we can define in the function signature. We have the below 4 types of Arguments:

  • Positional Arguments

  • Unnamed positional Arguments / VarArgs

  • Keyword-only Arguments

  • Keyword arguments / Varkwargs

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