Python Basics

Topics Covered

Sr. No.	Topic Name
1.	Types of data
2.	Expressions and variables
3.	String, Tuple, List, Dictionary, Set
4.	Loops
5.	Conditional Statements
6.	Functions and scope
7.	Objects and Classes and Dunder Methods
8.	__name__ == __main__
9.	*args and **kwargs
10.	Try, Except, Else and Finally (Exception handling)
11.	Virtual Enviroment
12.	Iterators, Iterables and Generators
13.	List, Set, Generator and Dictionary Comprehension
14.	Map, Reduce, Filter and Join
15.	Bisect Module
16.	Lambda Function
17.	Enumerate
18.	Formatting of string
19.	! Property, Decorators, Settters and Getters

1. Data Types

Everything in Python is an Object

Data Types :-
int : Integer Number ; float : Decimal Number ; str : String (Collection of characters) ; bool : True or False value

Typecasting is supported in python. Example: int(2.1) = 2.

boolean = True
Integer = 2
Float = 2.0
String = 'This is String'

print(boolean, Integer, Float, String ) 

# Typecasting

print('Float To Integer :' ,int(2.1))
print('Float to Integer: ',float(2))

# type() is used to print the class/data-type of variable

print(type(5))

# int('A') will not be typecasted

2. Expression and Variables

Expression: Statement consists of operators and operands to perform certain operation.

Variables: Used to store data in programming language.

3. String, List, Tuple, Dictionary, Set

String: Sequence of characters that is denoted under "" or ''. Example: "Name". Immutable(can't change the value of string but can overwrite it) , Ordered Sequence. Stride => [start:stop:jump]

Some Examples of String Methods are :-

1. .upper( ) : Convert to uppercase.
2. .replace('old_subset','new_subset') : replace the subset of string.
3. .find('subset') : returns -1 if not present.

List: Iterable object, ordered sequence, mutable object and denoted by [ ].Example: [1,3,4,2].

Some Examples of List methods are :-

1. .extend( )
2. .sort()
3. .split("delimiter")

del object name can delete any object in python.

Tuple: Immutable, ordered object and denoted by ( ). Example: (1,2,3).
Set: Unordered object, contains unique value and is represented by { }. Example: {1,2,3}.

1. .add('')
2. .remove('')
3. .union(set_name)

Dictionary: Contains keys and values, acts as hash map, keys have to be immutable and unique and values can be mutable. Example: {'a':1,'b':2}

1. .keys()
2. .values()
3. .items()

name in dictionary name will lookup for name in keys

4. Loops

There are three types of loop in python.

1. For
2. While

5. Conditional Statements

Relational Operators : >=, <=, ==, ===, !=; Logical Operators: AND, OR, NOT; Arithmetic Operators: +, - ,/, %, //

if (condition 1):
    block of statements
elif (condition 2):
    block of statements
else:
    block of statements

6. Functions and Scope

Function: Block of statement that have to execute agian and again. Syntax :-

def function_name(parameters):
    block of statements
    return value

Scope: Variables that is used in particular block of statements. if variable is not declared in function then it store the global value of that variable.

7. Objects and Classes

Class: Blueprint of Object, and Object: Instance of Class.

Every object has :-

1. a type.
2. an internal data representation Blueprint.
3. set of procedures for interacting with objects Methods.

_A class or types Methods are function that every instance of that class or type provides.

Syntax :- class_name__dict__ is used to show all the variables and methods in class_name class.

class ClassName: # Parent classes can be multiple or none according to the need.
    
    # Class variable - variable that is used by only this class.
    variable_name = value

    # Constructor
    def __init__(self, instanceVariables):
        self.instanceVariable = instanceVariable

    # Class Methods - method used by class only.
    @classmethod
    def class_method_name(cls, value): # used to change value of class variable
        cls.variable_name = value

    # Static methods - when there is no use of class or instance method
    @staticmethod
    def static_method_name(parameters):
        block of statements
  
# Inheritance 

class ClassName(ParentClass):
    
    def __init__(self,parameters_1, parameters_2):
        # if parameters_1 is present in parent class then we can inherit that class.
        super().__init__(parameters_1):
            self.parameters_2 = parameters_2
    
    # Same methods name can be used to overwrite methods of parent class. First class searches method in present class and after that it searches methods in parent class.


# Magic / Dunder Methods : used for method override and represented "__methodname__".

__add__ : To override addition. Example: (A + B)
__repr__: To cahnge representation of object. Example: repr(object_name) 
__str__: To overwrite repr() method. Example: str(object_name)

8. name == 'main'

It is best to use name == 'main' in python coding to run particular section of code from particular package and modules. name is global variable

if __name__ == '__main__':
    main()

def main():
    block of statements    

9. *args and **kwargs

*args: To take number of variables as an argument. Multiple one value pass. type(*args) = tuple
**kwargs: To take two values each time. Multiple Two Value pass. type(**kwargs) = dictionary

We can change names of args and kwargs but not notation.

10. Exception Handling

Exception: only interrupts certain part of program. Error: interrupts whole executable program.
try, except is used to handle exceptions in python.

Syntax :-

# Exception handling for multiple exceptions

try:
    error statement
except error_name as e:
    block of statements
except error_name as e:
    block of statements
.
.
.
finally: # This will run every time
    block of statements

# Exception handling with else

try:
    statement
except Exception as e:
    print(e)
else:
    print("if except block doesn't execute")
finally:
    print('This will always execute')

11. Virtual Enviroment

To use certain packages in certain project.

All commands here are for windows cmd/powershell.

To install virtualenv :-

pip install virtualenv

To create and activate virtual env :-

virtualenv virtualenv_name
virtualenv_name/scripts/activate

To deactivate virtual env :-

deactivate

To create requirements.txt file to hold all required package name :-

pip freeze>requirements.txt

To create virtual env which have preinstalled system packages :-

virtualenv --system-site-package virtualenv_name

To delete virtual env :-

del virtualenv_name

To install packages that are in requirements.txt :-

pip install -r requirements.txt

12. Iterators, Iterables and Generators

• Iterator : operator used for iteration.
• Iterable : object that can be iterated.
• Iteration: process of iterating elements.
• Generator: takes time but doesn't consume much memory, very useful to create iterable object.

iter()is used to create iterable object.

Python code :-

# Generator

def gernerator_name(parameters):
    for i in range(200):
        yield i
print(gen(1000))

obj_1 = gen(1000)
obj_1.next() # To yield next item of generator object

13. List, Set, Dictionary and Generator Comprehension

List Comprehension

list_object = [ ]
[function for parameters in list_object if condition] 

Dictionary Comprehension

dict_1 = { }
{function for parameters in list_object if condition}

Set Comprehension

set_1 = set()
{function for parameters in list_object if condition} 

Generator Comprehension

gen = (function for parameters in list_object if condition)
for item in gen:
    print(item)

14. Map, Filter, Reduce and join in Python

• Map: return map object , map each element of sequence to the given function.Syntax: map (function_to_apply, list_of_inputs)
• Reduce: return list object, reduce the number of elements in sequence by applying function to each element of the sequence.Syntax: First import : from functools import reduce then reduce(function_name, list)
• Filter: return filter object, contains elements if the condition is true. We have to typecast the result.Syntax: filter(function_name, list_of_inputs)
• Join: Join each elements in list with some symbol.Syntax: 'symbol'.join(list_of_inputs)

15. Bisect Module in Python

Doesn't sort so sorted list is required. It is used to insert number in the list such that the after insertion list remains sorted. Uses Binary Search.

Syntax:-

import bisect
bisect.bisect(list_of_number, value_to_be_inserted) # tells ehere to insert number
bisect.insort(list_of_number, value_to_be_inserted) # inserts the number

16. Lambda function in Python

One Line function also known as anonymous function and generally used when we want to use function onlhy one time.

Syntax:-

variable_name = lambda parameters : statement

17. Enumerate in Python

To convert to the number. Syntax :-

list1 = [ 'a','b','c' ]
for i,item in enumerate(list_1):
    print(i,'->',item) 

18. Formatting of string in Python

used to format the template for string in python. Example :-

name = 'Algorithm To Live By'
categ = 'non-fiction'
template = 'This is {} book and category of this book is {}'.format(name,categ)
template = 'This is {1} book and category of this book is {0}'.format(name,categ)

Python OOPS Library Example

1. Change branch to Python_OOPS_Example
2. Open Python_OOPS.py

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