Python Functions

Walter Kibet — Tue, 03 Aug 2021 20:19:59 +0000

A function is a block of code which only runs when it is called.

You can pass data, known as parameters, into a function.

A function can return data as a result.

Creating a Function

In Python a function is defined using the def keyword:

def my_function():
  print("Hello from a function")

Calling a Function

To call a function, use the function name followed by parenthesis:

Example

def my_function():
  print("Hello from a function")

my_function()

Arguments

Information can be passed into functions as 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.

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:

Example

def my_function(fname):
  print(fname + " Refsnes")

my_function("Emil")
my_function("Tobias")
my_function("Linus")

Arguments are often shortened to args in Python documentations.

Parameters or Arguments?
The terms parameter and argument can be used for the same thing: information that are passed into a function.

From a function's perspective:

A parameter is the variable listed inside the parentheses in the function definition.

An argument is the value that is sent to the function when it is called.

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.

Example
This function expects 2 arguments, and gets 2 arguments:


def my_function(fname, lname):
  print(fname + " " + lname)

my_function("Emil", "Refsnes")

If you try to call the function with 1 or 3 arguments, you will get an error:
Example
This function expects 2 arguments, but gets only 1:


def my_function(fname, lname):
  print(fname + " " + lname)

my_function("Emil")

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.

This way the function will receive a tuple of arguments, and can access the items accordingly:

Example
If the number of arguments is unknown, add a * before the parameter name:


def my_function(*kids):
  print("The youngest child is " + kids[2])

my_function("Emil", "Tobias", "Linus")

Arbitrary Arguments are often shortened to *args in Python documentations.

Keyword Arguments

You can also send arguments with the key = value syntax.

This way the order of the arguments does not matter.

Example

def my_function(child3, child2, child1):
  print("The youngest child is " + child3)

my_function(child1 = "Emil", child2 = "Tobias", child3 = "Linus")

The phrase Keyword Arguments are often shortened to kwargs in Python documentations.

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.

This way the function will receive a dictionary of arguments, and can access the items accordingly:

Example
If the number of keyword arguments is unknown, add a double ** before the parameter name:

def my_function(**kid):
  print("His last name is " + kid["lname"])

my_function(fname = "Tobias", lname = "Refsnes")

Arbitrary Kword Arguments are often shortened to **kwargs in Python documentations.

Default Parameter Value

The following example shows how to use a default parameter value.

If we call the function without argument, it uses the default value:

Example

def my_function(country = "Norway"):
  print("I am from " + country)

my_function("Sweden")
my_function("India")
my_function()
my_function("Brazil")

Passing a List as an Argument

You can send any data types of argument to a function (string, number, list, dictionary etc.), and it will be treated as the same data type inside the function.

E.g. if you send a List as an argument, it will still be a List when it reaches the function:

Example

def my_function(food):
  for x in food:
    print(x)

fruits = ["apple", "banana", "cherry"]

my_function(fruits)

Return Values

To let a function return a value, use the return statement:

Example

def my_function(x):
  return 5 * x

print(my_function(3))
print(my_function(5))
print(my_function(9))```
{% endraw %}


##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.

Example
{% raw %}

```python
def myfunction():
  pass

Python Basics, Python 101

Walter Kibet — Sat, 24 Jul 2021 21:18:01 +0000

Introduction

Python is a general-purpose interpreted, interactive, object-oriented, and high-level programming language. It was created by Guido van Rossum during 1985- 1990. Like Perl, Python source code is also available under the GNU General Public License (GPL)

Why to Learn Python?

Python is a high-level, interpreted, interactive and object-oriented scripting language. Python is designed to be highly readable. It uses English keywords frequently where as other languages use punctuation, and it has fewer syntactical constructions than other languages.
Python is a MUST for students and working professionals to become a great Software Engineer specially when they are working in Web Development Domain. I will list down some of the key advantages of learning Python:
• Python is Interpreted − Python is processed at runtime by the interpreter. You do not need to compile your program before executing it. This is similar to PERL and PHP.
• Python is Interactive − You can actually sit at a Python prompt and interact with the interpreter directly to write your programs.
• Python is Object-Oriented − Python supports Object-Oriented style or technique of programming that encapsulates code within objects.
• Python is a Beginner's Language − Python is a great language for the beginner-level programmers and supports the development of a wide range of applications from simple text processing to WWW browsers to games

Python is popular because of the following reasons

Easy-to-learn
Easy-to-read
Easy-to-maintain
A broad standard library
Python supports GUI Programming
Python provides interfaces to all major commercial databases
Python can run on a wide variety of hardware platforms

Applications of Python

• Artificial Intelligence
• Desktop Application
• Automation
• Web Development
• Data Analysis and Visualization

Installation

Download python from here.

IDEs

Popular IDEs include
• PyCharm
• Kite
• Spyder
• IDLE
• Sublime Text 3
• Visual Studio Code
• Atom

Hello World using Python

console.log('markdown')
print ("Hello, Python!")

DEV Community: Walter Kibet

Python Functions

Creating a Function

Calling a Function

Arguments

Number of Arguments

Keyword Arguments

Arbitrary Keyword Arguments, **kwargs

Default Parameter Value

Passing a List as an Argument

Return Values

Python Basics, Python 101

Introduction

Why to Learn Python?

Python is popular because of the following reasons

Applications of Python

Installation

IDEs

Hello World using Python