Python Basics

Introduction

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:

Hello World

The first program that every programmer writes is called "Hello World". It's a simple program that prints Hello, World! to the screen. Here's how you can do this in Python:

print("Hello, World!")

Hello, World!

Python Indentation

Python uses indentation for blocks, instead of curly braces. Both tabs and spaces are supported, but the standard indentation requires standard Python code to use four spaces. For example:

if 5 > 2:
    print("Five is greater than two!")

Python Syntax

python is a non-strict language, which means that you don't have to declare the type of a variable when you create one. Python automatically assigns the data type according to the value you assign. For example:

x = 5
y = "Hello, World!"
z = 5.0
a = True
b = []

Python Variables

Variables are containers for storing data values. Python has no command for declaring a variable. There are 2 types of variables in Python:

• Local Variables: A variable declared inside a function is known as a local variable.
• Global Variables: A variable declared outside a function is known as a global variable.

In python, you don't have to declare the type of variable, it can be declared with or without assigning a value. For example:

x = 5
y = "Hello, World!"

Global Variables

Global variables are the one that are defined and declared outside a function and we need to use them inside a function. For example:

x = "awesome"
 
def myfunc():
    print("Python is " + x) # x is a global variable
 
myfunc()

Python is awesome

Local Variables

A variable declared inside a function is known as a local variable. A local variable can only be used inside a function where it is declared. For example:

def myfunc():
    y = "fantastic"
    print("Python is " + y) # y is a local variable
 
myfunc()

Python is fantastic

Rule of Thumb

• A variable name must start with a letter or the underscore character.
• A variable name cannot start with a number.
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ).
• Variable names are case-sensitive (age, Age and AGE are three different variables).

Tips & Tricks

• You can assign multiple values to multiple variables in one line. For example:

x, y, z = "Orange", "Banana", "Cherry"
print(x)
print(y)
print(z)

Orange
Banana
Cherry

• You can assign the same value to multiple variables in one line. For example:

x = y = z = "Orange"
print(x)
print(y)
print(z)

Orange
Orange
Orange

• When you are using a global variable inside a function, you can use the global keyword to make the variable global. For example:

x = "awesome"
 
def myfunc():
    global x
    x = "fantastic"
 
def Main():
    print("Python is " + x)
    myfunc()
    print("Python is " + x)

Python is awesome
Python is fantastic

• When you are using a global variable inside a function, I recommend you to assign the value to a local variable and use it. For example:

x = "awesome"
 
def myfunc():
    y = x
    y = "fantastic"
    print("Python is " + y)
 
def Main():
    print("Python is " + x)
    myfunc()
    print("Python is " + x)

Python is awesome
Python is fantastic
Python is awesome