Python Quick Reference

It is a quick reference for seasoned developer, who already master at least one programming language. for myself, I have worked with C# for more than 10+ years. this reference can help you easily translate from other language to python

Naming Variables : camel Case

    myVariable

Data Types: 

    Text Type: 

         str "hello world"

    Numeric Types: 

        int : (10),

        long :(101L)

        float: (10.01), 

        complex: (3j)

    Sequence Types:

        list: ["a","b","c","d"], 

        tuple: immutable 

        myTuple = ("a","b","c","d")  

       tuple[0]="New assignment"  TypeError: 'tuple' object does not support item assignment

        range: generate a sequence of integer

        range(5) : 0 1 2 3 4

        range(0, 5, 2) : 0 2 4

    Mapping Type: 

        dictionary: list of key value pairs

        myDictionary={"key1:value1, "key2:value2 }

    Set Types:

    set 

    frozenset

Boolean Type: bool

Binary Types: bytes, bytearray, memoryview

Comments

    # single comment

    """

    multiple line comments

    another line comments

    """

Strings

Multiline and Formatting Strings

Indentation

Arithmetic Operators

Comparison Operators

    <, >, <=, >=, ==, !=, <>

Logical Operators

    and, or, not

Assignment Operators

    a=b assign value from right to left

    a +=b a=a+b

    a -=b a=a-b

   a *=b a=a*b

    a /=b a=a/b

    a **=b a=a**b

    a //=b   a=a//b   10 //=3   => 10//3=3

 If Statements

    if condition:

    elif condition:

    else:

Ternary If Statements

    message= "true condition" if condition else "false condition"

Lists

    operators:

        Length: len([1, 2, 3] => 3

        Concatenation: ["a", "b", "c"] + [1, 2, 3]  => ["a", "b", "c", 1, 2, 3]

        Repetition: [a, b] * 3 => ["a", "b", "a", "b", "a", "b"]

        Slicing [1: ]   myList=[1,  2,  3] myList[1:] => [2, 3]

        Indexing :

        myList=[1,  2,  3]  

        offsets starting from zero:  myList[1] => 2

         if negative counting from the right side:  myList[-1] => 3

      Built in List methods 

          max(myList) =>3

          min(myList) => 1

         list: convert  iterable object into a list

         list("abcd")=>[a, b, c, d]

         list(123456) TypeError: 'int' object is not iterable

         list("123456") => [1, 2, 3, 4, 5 ,6]

         list({12, "ab", [1, 3]}) => [12, "ab", [1, 3]]

Useful List Methods

• append : add item the end of the list
• count: find the number of occurrence of object
• extend: append iterable object to the list
• insert: add item to the offset index
• pop: return the item from the list
• remove: remove item from the list
• reverse: reverse the order of items in the list
• sort: sort items in the list

Deleting Items from Lists

    del list(obj) exactly like list.remove(obj)

Sets

    not allow to have duplicate item

Set Union Intersection & Difference

    union : setA | setB

    intersect: setA & setB

    differece: setA - setB

    symmetric_difference: setA ^ setB

Dictionaries

    key value pairs data structure

   myDict ={

        "key1" : value1, 

        "key2" : value2,

        "key3" : value3

}

value1=myDict["key1"]

    Functions:

        len:

        

    Methods:

For Loops

    for item in list or set:

        print(item)

Loop Through Dictionaries

    for key in dict: 

        print(f"key: {key} value: {dict[key]}")

While Loop

    number=0

    while number < 3

         number +=1

Break and Continue

    break: exist the the loop if condition meets

              number=0

                while number < 3

                     if number==2

                        break;

                     number +=1

    continue: continue the loop if the condition is true

                       number=0

                            while number < 3

                     if number <=2

                            continue;

                            number +=1

Functions 

    def myfunction():

        print("this  is my first function")

Built in Functions and Import Statement

    import python module: 

        import math

    import specific method from the module

        from math import floor

Creating Modules

        create a python file myModule.py

        in another file use import myModule to reference the moudule

         printing all variables and function names of the "myModule" module

          dir(myModule)

Classes and Objects

    classes are the blueprints of objects

    objects are the instances of classes

Creating Classes and Objects

     class person

        #define the constructor

        def __init__(self, firstName,lastName):

                self.fistName=firstName

                self.lastName=lastName 

     myObject=person("first name", "last name")

 Inheritance

    class driver(person)  #driver is inherited from person

Printing Objects

    # override method

    def __str__(self) -> str:

           return f"last name: {self.firstName}, last name: {self.lastName}"

Working With Dates

    from datetime import datetime #work with datetime

    from datetime import date    #work with actual date

Formatting Dates

    now=datetime.now()

    now.strftime("datetime string formatter") 

Creating Files

    file =open("./myfile.txt", "w")      # create a text file myfile.txt in the current working dir

    flags: a -> append

              r -> read

              r+ -> read and write

              w -> write

    file.close() # to properly close the file being read or write    

Reading From Files

     file =open("./myfile.txt", "r") 

     file.read()

     file.close()

A Better Way To Work With Files

    import os.path

    if(os.path.isfile(myfile.txt):  #ensure the file exists before read write operations

            with open("./myfile.txt", "r")  as file

                file.read()

Fetching Data From Internet

     import json

    from urllib import request

    response = request.urlopen(("https://fakerapi.it/api/v1/companies?_quantity=5"))

    resjson = json.loads(response.read())

    print(resjson["data"])

Pip & Modules

    pip3: python package manager

    pip3 install requests

 Request Module

    import json

    import requests

    response = requests.get(("https://fakerapi.it/api/v1/companies?_quantity=5"))

    print(response.text)

    jsonData = json.loads(response.text)

    print(jsonData["data"])

Text To Speech

  pip3 install pyttsx3

   import pyttsx3

   pyttsx3.speak

Asterik * 

 * is argument-unpacking and ** keyword-argument-unpacking operators

The single star * unpacks the sequence/collection into positional arguments

The double start ** uses a dictionary and thus named arguments.