Python Introduction

Python is a popular programming language. It was created by Guido van Rossum, and
released in 1991.

It is used for:

 web development (server-side),

 software development,
 mathematics,
 system scripting.

 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 Syntax compared to other programming

languages
 Python was designed for readability, and has some similarities to the English
language with influence from mathematics.
 Python uses new lines to complete a command, as opposed to other programming
languages which often use semicolons or parentheses.
 Python relies on indentation, using whitespace, to define scope; such as the scope of
loops, functions and classes. Other programming languages often use curly-brackets
for this purpose.

Example

print("Hello, World!")

Python Indentation
Indentation refers to the spaces at the beginning of a code line.Where in other programming
languages the indentation in code is for readability only, the indentation in Python is very
important.Python uses indentation to indicate a block of code.

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

Python will give you an error if you skip the indentation:

Example

Syntax Error:

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

The number of spaces is up to you as a programmer, the most common use is four, but it has
to be at least one.

Example

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

You have to use the same number of spaces in the same block of code, otherwise Python will
give you an error:

Example

Syntax Error:

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

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

Example
#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:

Example

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

A comment does not have to be text that explains the code, it can also be used to prevent
Python from executing code:

Multi Line Comments

Python does not really have a syntax for multi line comments.

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

Example

#This is a comment
#written in
#more than just one line
print("Hello, World!")

Or, not quite as intended, you can use a multiline string.

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:

Example

"""
This is a comment
written in
more than just one line
"""
print("Hello, World!")

As long as the string is not assigned to a variable, Python will read the code, but then ignore
it, and you have made a multiline comment.
 VARAIBLES IN PYTHON

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.

Example

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

Variables do not need to be declared with any particular type, and can even change type after
they have been set.

Example

x=4 # x is of type int

x = "Sally" # x is now of type str
print(x)

Single or Double Quotes

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

Example

x = "John"
# is the same as
x = 'John'
 Case-Sensitive
Variable names are case-sensitive.

Example

This will create two variables:

a=4
A = "Sally"
#A will not overwrite a

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

Example :-

Correct variable names:

myvar = "John"

my_var = "John"

_my_var = "John"
myVar = "John"

Example

Wrong variable names:

2myvar = "John"

my-var = "John"

my var = "John"

Many Values to Multiple Variables

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

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

print(x)

print(y)

print(z)

Single Values to Multiple Variables

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

Example:-
x=y=z=1

Print(y)
 Python - Output Variables
The Python print() function is often used to output variables.

Example

x = "Python is awesome"
print(x)

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

Example

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

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

Example

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

Notice the space character after "Python " and "is ", without them the result would be
"Pythonisawesome".

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

Example

x=5
y = 10
print(x + y)
 In the print() function, when you try to combine a string and a number with the + operator,
Python will give you an error:

Example

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:

Example

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

Python Data Types

Built-in Data Types
In programming, data type is an important concept.

Variables can store data of different types, and different types can do
different things.

Python has the following data types built-in by default, in these

categories:
 Text Type: str

Numeric Types: int, float, complex

Sequence list, tuple, range

Types:

Mapping Type: dict

Set Types: set

Getting the Data Type

You can get the data type of any object by using the type() function:

Example

Print the data type of the variable x:

x=5

print(type(x))

Output:-

<class ‘int’>

Setting the Data Type

In Python, the data type is set when you assign a value to a variable:

Example Data Type

x = "Hello World" str

x = 20 int

x = 20.5 float

x = 1j complex

x = ["apple", "banana", "cherry"] list

x = ("apple", "banana", "cherry") tuple

x = {"name" : "John", "age" : 36} dict

x = {"apple", "banana", "cherry"} set

Python Numbers

There are three numeric types in Python:

 int
 float
 complex

Variables of numeric types are created when you assign a value to them:
Example:-

x=1 # int

y = 2.8 # float
z = 1j # complex

Int

Int, or integer, is a whole number, positive or negative, without decimals, of

unlimited length.

Example

Integers:

x=1

y = 35656222554887711

z = -3255522

print(type(x))

print(type(y))

print(type(z))

Output:-
<class 'int'>
<class 'int'>
<class 'int'>

Float

Float, or "floating point number" is a number, positive or negative,

containing one or more decimals.

Example

Floats:

x = 1.10

y = 1.0

z = -35.59

print(type(x))

print(type(y))

print(type(z)

Complex
Complex numbers are written with a "j" as the imaginary part

Example

Complex:

x = 3+5j

y = 5j

z = -5j

print(type(x))

print(type(y))

print(type(z))

Type Conversion

You can convert from one type to another with the int(), float(),
and complex() methods:

Example:-#convert from int to float:

x = float(1)
#convert from float to int:

y = int(2.8)

#convert from int to complex:

z = complex(x)

print(x)

print(y)

print(z)

print(type(x))

print(type(y))

print(type(z))

Output:-

1.0
2
(1+0j)
<class 'float'>
<class 'int'>
<class 'complex'>

Type Conversion
 You can convert from one type to another with the int(), float(), and complex() methods:

Example

Convert from one type to another:

x = 1 # int
y = 2.8 # float
z = 1j # complex

#convert from int to float:

a = float(x)

#convert from float to int:

b = int(y)

#convert from int to complex:

c = complex(x)

print(a)
print(b)
print(c)

print(type(a))
print(type(b))
print(type(c))

Note: You cannot convert complex numbers into another number type.

Random Number
Python does not have a random() function to make a random number, but Python has a built-
in module called random that can be used to make random numbers:

Example

Import the random module, and display a random number between 1 and 9:

import random

print(random.randrange(1, 10))
 Python Casting
Specify a Variable Type
There may be times when you want to specify a type on to a variable. This can be done with
casting. Python is an object-orientated language, and as such it uses classes to define data
types, including its primitive types.

Casting in python is therefore done using constructor functions:

 int() - constructs an integer number from an integer literal, a float literal (by
removing all decimals), or a string literal (providing the string represents a whole
number)
 float() - constructs a float number from an integer literal, a float literal or a string
literal (providing the string represents a float or an integer)
 str() - constructs a string from a wide variety of data types, including strings, integer
literals and float literals

Example

Integers:

x = int(1) # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3

Example

Floats:

x = float(1) # x will be 1.0

y = float(2.8) # y will be 2.8
z = float("3") # z will be 3.0
w = float("4.2") # w will be 4.2

Example

Strings:
x = str("s1") # x will be 's1'
y = str(2) # y will be '2'
z = str(3.0) # z will be '3.0'