Python tutorial For Beginner

 What is Python?

Python is a popular programming language.

Python can be used on a server to create web application


It is used for:


web development (server-side),

software development,

mathematics,

system scripting.

What can Python do?

Python can be used on a server to create web applications.

Python can be used alongside software to create workflows.

Python can connect to database systems. It can also read and modify files.

Python can be used to handle big data and perform complex mathematics.

Python can be used for rapid prototyping, or for production-ready software development.

Why Python?

Python works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc).

Python has a simple syntax similar to the English language.

Python has syntax that allows developers to write programs with fewer lines than some other programming languages.

Python runs on an interpreter system, meaning that code can be executed as soon as it is written. This means that prototyping can be very quick.

Python can be treated in a procedural way, an object-oriented way or a functional way.


Python Comments


Comments can be used to explain Python code.


Comments can be used to make the code more readable.


Comments can be used to prevent execution when testing code.

Comments starts with a #, and Python will ignore them:

#This is a comment

print("Hello, World!")


Comments can be placed at the end of a line, and Python will ignore the rest of the line:

print("Hello, World!") #This is a comment



Multiline Comments

Python does not really have a syntax for multiline comments.


To add a multiline comment you could insert a # for each line:


#This is a comment

#written in

#more than just one line

print("Hello, World!")



Since Python will ignore string literals that are not assigned to a variable, you can add a multiline string (triple quotes) in your code, and place your comment inside it:


"""

This is a comment

written in

more than just one line

"""

print("Hello, World!") 


Variables

Variables are containers for storing data values.


Creating Variables

Python has no command for declaring a variable.

A variable is created the moment you first assign a value to it.


x = 4       # x is of type int

x = "Ram" # x is now of type str

print(x)


Case-Sensitive

Variable names are case-sensitive.


a = 4

A = "Sally"

#A will not overwrite a

Casting

If you want to specify the data type of a variable, this can be done with casting.

x = str(3)    # x will be '3'

y = int(3)    # y will be 3

z = float(3)  # z will be 3.0


Get the Type

You can get the data type of a variable with the type() function.


x = 5

y = "John"

print(type(x))

print(type(y)


Single or Double Quotes?

String variables can be declared either by using single or double quotes:

x = "RAM"

# is the same as

x = 'RAM'


Variable Names

A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for Python variables:

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)

A variable name cannot be any of the Python keywords.

myvar = "Hello"

my_var = "Hello"

_my_var = "Hello"

myVar = "Hello"

MYVAR = "Hello"

myvar2 = "Hello"


Illegal variable names:


2myvar = "Hello"

my-var = "Hello"

my var = "Hello"


Remember that variable names are case-sensitive


Many Values to Multiple Variables


Python allows you to assign values to multiple variables in one line:


x, y, z = "Orange", "Banana", "Cherry"

print(x)

print(y)

print(z)


Many Values to Multiple Variables

Python allows you to assign values to multiple variables in one 

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


Note: Make sure the number of variables matches the number of values, or else you will get an error

And you can assign the same value to multiple variables in one line:

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


Unpack a Collection

If you have a collection of values in a list, tuple etc. Python allows you to extract the values into variables. This is called unpacking.


fruits = ["apple", "banana", "cherry"]
x, y, z = fruits
print(x) // apple
print(y) // banana
print(z) // cherry


In the print() function, you output multiple variables, separated by a comma:

x = "Python"
y = "is"
z = "awesome"
print(x, y, z) // Python is awesome


You can also use the + operator to output multiple variables:

x = "Python "
y = "is "
z = "awesome"
print(x + y + z) // Python is awesome

For numbers, the + character works as a mathematical operator:

x = 5
y = 10
print(x + y) // 15

In the print() function, when you try to combine a string and a number with the + operator, Python will give you an error:

x = 5
y = "John"
print(x + y)

The best way to output multiple variables in the print() function is to separate them with commas, which even support different data types:

x = 5
y = "John"
print(x, y) // 5 John


Global Variables

Variables that are created outside of a function (as in all of the examples in the previous pages) are known as global variables.

Global variables can be used by everyone, both inside of functions and outside.


x = "awesome"

def myfunc():
  print("Python is " + x)

myfunc() // Python is awesome


If you create a variable with the same name inside a function, this variable will be local, and can only be used inside the function. The global variable with the same name will remain as it was, global and with the original value.

x = "awesome"

def myfunc():
  x = "fantastic"
  print("Python is " + x) // Python is fantastic 

myfunc()

print("Python is " + x) //Python is awesome


The global Keyword

Normally, when you create a variable inside a function, that variable is local, and can only be used inside that function.

To create a global variable inside a function, you can use the global keyword.


def myfunc():
  global x
  x = "fantastic"

myfunc()

print("Python is " + x)















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