# Introduction to Python

![Introduction to Python](https://cdn.hashnode.com/res/hashnode/image/upload/v1680988432101/23d3dd7c-3e65-4b44-90d5-6c4249ee3ae9.png)

Python is an interpreted, high-level, general-purpose programming language. Created by Guido van Rossum and first released in 1991, Python’s design philosophy emphasizes code readability with its notable use of significant whitespace. Since I am taking a course on introduction to python at the time of writing, what better way to document it than to write about it!? Btw, I’m gonna be trying to build a port scanner in python at the end of the course! (That will be a separate writeup hehe) So…lets get started!

* * *

Strings
=======

*   To print basic text

    #!/bin/python3  
    #Print string print("Hello, world!") 
    print('Hello, world!')

*   To print multiline text

    print("""This string runs 
    multiple lines dood!""")

*   To print 2 string concatenated together

    print("This string is "+"awesome!")
    

*   To add an empty line spacing in-between outputs

    #!/bin/python3  
    #Print string print("Hello, world!") 
    print('\n') #adds new line 
    print('Hello, World!')

* * *

Math
====

*   Basic operations

    #!/bin/python3  
    #Math 
    print(50 + 50) #addition 
    print(50 - 50) #subtraction 
    print(50 * 50) #multiplication 
    print(50 / 50) #division

*   Advanced operations

    print(50 + 50 - 50 * 50 / 50) #pemdas 
    print(50 ** 2) #exponents 
    print(50 % 6) #modulo 
    print(50 // 6) #returns whole number

* * *

Variables & Methods
===================

*   Declaring a variable and using it later in the program

    #!/bin/python3  
    #Variables & Methods 
    quote = "Control is an illusion" 
    print(quote)

*   Using methods to modify the output

    print(quote.upper()) #uppercase 
    print(quote.lower()) #lowercase 
    print(quote.title()) #title 
    print(len(quote)) #length of variable

*   Using methods to get properties/values of a certain type

    print(len(quote)) #length of variable  
    name = "Neeranjan" #String 
    age = 19 #int int(19) 
    height = 1.8 #float float(1.8)  
    print (int(age)) 
    print (int(height))

*   Using methods to manipulate the output of text

    print("My name is " + name + "and I am " + str(age) + "years old. I am also " + str(height) + "m tall")

*   Increment variable by a certain amount

    age += 1 #increase age variable by 1
    print(age)
    birthday = 1 #increase age variable by birthday variable
    age += birthday
    print(age)

* * *

Functions
=========

*   Defining a function

    #Functions
    print("\nFunctions--")
    def whoAmI(): #This is a function
     name = "Neeranjan" #String
     age = 19 #int int(19)
     height = 1.8 #float float(1.8)
     print("My name is " + name + "and I am " + str(age) + "years old. I am also " + str(height) + "m tall")

*   Running a function

    whoami()

*   Adding parameters to a function

    #adding parameters
    def addOneHundred(num):
     print(num+100)
     
    addOneHundred(50)
    
    #adding multiple parameters
    def addition(x,y):
     print(x + y)
     
    addition(50,55)
    
    def multiply(x,y):
     return x * y #returning value to method != printing
     
    print(multiply(5,5))
    
    def squareRoot(x):
     print(int(x ** 0.5))
     
    squareRoot(64)

*   Creating functions to speed up simple yet time-consuming tasks

    def nl():
     print('\n')
    
    
    nl()

Boolean Expressions (T/F)
=========================

*   Creating basic Boolean expressions that will either return true or false

    #Boolean Expressions
    print("\nBoolean Expressions--")
    bool1 = True
    bool2 = 3*3 == 9
    bool3 = False
    bool4 = 3*3 != 9
    print(bool1, bool2, bool3, bool4)
    print(type(bool1))

*   Differentiating between STRING True and BOOLEAN

    #Boolean Expressions
    print("\nBoolean Expressions--")
    bool1 = True
    bool5 = "True"
    print(type(bool1))
    print(type(bool5))

* * *

Relational and Boolean operators
================================

*   Creating Boolean statements / Variables

    nl()
    #Relational and Boolean operators
    print("\nRelational and Boolean operators--")
    greaterThan = 7 > 5
    lessThan = 5 < 7
    greaterThanEqualTo = 7 >= 7
    lessThanEqualto = 7 <=7
    #All of the above statements will return True (boolean)

*   Creating statements with AND, OR & NOT

    testAnd = (7 > 5) and (5 < 7)  #AND = true statement + true statement will make the whole thing return True
    testAnd2 = (7 > 5) and (5 > 7) #AND = true statement + false statement will make the whole thing return False
    
    testOr = (7 > 5) and (5 < 7)  #OR = true statement + true statement will make the whole thing return True
    testOr2 = (7 > 5) and (5 > 7) #OR = true statement + false statement will make the whole thing return True
    
    testNot = not True #Returns False
    testNot2 = not False #Returns True

*   Refer to Truth table

![Introduction to Python](https://cdn.hashnode.com/res/hashnode/image/upload/v1680988433934/1d537c17-8624-44d1-8fcf-1ab98e5d3335.png)

* * *

Conditional Statements
======================

*   Building a simple IF statement

    nl()
    #Conditional statements
    print("\nConditional statements--")
    
    def buyDrink(money):
     if money >= 2:
      return "You've got yourself a drink"
     else:
      return "No drink for you!"
      
    print(buyDrink(10))
    print(buyDrink(1.5))

*   Building an advance IF statement with multiple conditions

    def buyBeer(age,money):
     if (age >= 21) and (money >= 5):
      return "Here is your cold beer!"
     elif (age >= 21) and (money < 5):
      return "Sorry you do not have enough money"
     elif (age < 21) and (money >= 5):
      return "Nice try, kid!"
     else:
      return "You're young, dumb and broke!"
     
    print(buyBeer(21,5))
    print(buyBeer(20,4))
    print(buyBeer(20,5))

* * *

Lists
=====

*   Declaring a simple list and then printing it

    nl()
    
    #Lists - Have brackets []
    print("\nLists--")
    
    shows = ["Mr. Robot", "Money Heist", "Locke and key", "Orange is the new Black"]
    
    print(shows[0]) #Item one in a list is always 0
    print(shows[1])
    print(shows[0:3]) #Pulls out all values just b4 the last index
    print(shows[0:4]) #Pulls out all the values in the list
    print(shows[2:])  #Pulls out all the values after the index specified
    print(shows[:1])  #Pulls out all the values before the index specified / grabbing 1 item from the list
    print(shows[-1])  #Pulls out the last value in the list
    #print(len(shows)) #prints the number of items in the list

*   Adding to and removing from the list

    shows.append("Sex education")
    print(shows)
    
    shows.pop() #removes the last item in the list
    print(shows)
    
    shows.pop(0)#removed the first item in the list
    print(shows)

* * *

Tuples
======

*   Declaring a tuple and printing it

    nl()
    
    #Tuples - Does not change, ()
    print("\nTuples--")
    
    grades = ("A", "B", "C", "D", "F")
    print(grades[1])

* * *

Looping
=======

*   For loop

    nl()
    
    #Looping
    print("\nLooping--")
    
    #For loops - start to finish of an iterate
    vegetables = ["cucumber", "spinach", "cabbage"]
    
    for x in vegetables:
     print(x)

*   While loop

    nl()
    
    #While loops - Executes as long as true
    i = 1
    
    while i < 10:
     print(i)
     i += 1

* * *

Importing modules
=================

*   Importing modules and using them in programs

    import sys #system function & parameters
    import os
    import datetime
    from datetime import datetime
    from datetime import datetime as dt #import with alias
    
    
    
    print(sys.version)
    
    print(datetime.now())
    
    print(dt.now())
    
    #argv == $1 in bash. 
    #sys.exit() #exits python cleanly

Advance strings
===============

*   Retrieve certain letters/words from certain word/sentence

    #Advance Strings
    print("\Advance Strings--")
    myName = "Neeranjan"
    
    print(myName[4]) #Retrieve a certain letter from the word
    print(myName[-1])
    
    sentence = "This is a sentence."
    print(sentence[:4]) #Retrieve a certain word from the sentence

*   Using the SPLIT and JOIN functions

    print(sentence.split()) #splits the sentence based on a delimiter
    
    splitSentence = sentence.split()
    joinSentence = ' '.join(splitSentence) #Joins the sentence back together using the provided delimiter. (space in this case)
    print(joinSentence)

*   Using quotes inside of a string variable

    quote = "He said, 'give me all your money'" 
    quote1 = "He said, \"give me all your money\""
    #both of these methods will work the same
    print(quote, quote1)

*   Stripping the extra space in a string

    tooMuchSpace = "           hello               "
    print(tooMuchSpace.strip())

*   Check for letter in word (case sensitive/non case sensitive)

    #case sensitive
    print("A" in "Apple") #True
    print("a" in "Apple") #False
    
    #non case sensitive
    letter = "A"
    word = "Apple"
    
    print(letter.lower() in word.lower())

\`

*   A better way to print text with variables in it

    show = "Mr. Robot"
    show2 = "Orange is the new black"
    print("My favourite shows are {} and {}.".format(show, show2))

* * *

Dictionary
==========

*   Declaring dictionary: assigning one value to a key (Key/Value Pairs)

    #Dictionaries - key/value pairs
    print("\Dictionary--")
    
    drinks = {"Orange Juice": 7, "Apple Juice": 10, "Lemon Juice": 8} #Drink = key; Price = value
    
    print(drinks)

*   Declaring dictionary: assigning multiple values to a key

    employees = {"Finance": ["Krista", "Susan", "Joanna"], "IT": ["Elliot", "Tyrell", "Darlene"], "HR": ["Leon", "Mr. Robot", "Phillip"]}
    
    print(employees)

*   Adding new key : value pair to an existing dictionary

    employees["Legal"] = ["Trenton"] #Add new key:value pair
    print(employees)
    
    employees.update({"Sales": ["Anddy", "Ollie"]}) #Add new key:value pair
    print(employees)

*   Updating an existing value in a dictionary

    drinks["Orange Juice"] = 8
    print(drinks)

*   Getting values from a dictionary

    print(employees.get("IT"))

![Introduction to Python](https://cdn.hashnode.com/res/hashnode/image/upload/v1680988435133/13a15fa5-16ea-4817-9cad-e11922461db3.png)