• https://www.learnpython.org/

• print - was a statement in Python2 whereas it is a function in Python3. It must be invoked with a parantheses. like, print("Hello World!");
• Python uses indentation for blocks, instead of curly braces. Both tabs and spaces are supported, but the standard indentation requires standard Python code to use four spaces.
• You can check the version of python using python --version in the command line or the terminal.

  ¿ python --version
  Python 3.8.0
  

Apart from the standard operators for addition (+), substraction (-), multiplication (*), division (/), and modulus (%), Python offers a few more as follows.

• Integer Division - //. As the division operator (/) always returns a decimal value (float), the Integer division helps to get the whole number.
• Exponentiation - **. An easy alternative for the math.pow(), which does the same thing. Example: 5 ** 2 gives the value of 25, which is 5 raised to the power of 2.
• Order of operations - Parentheses are meaningful in Python. When it comes to computation, Python always computes what is in parentheses first.
• Evaluation Rule - Similar to BODMAS, Python follows a different rule - PEMDAS - parentheses first, exponentiation second, multiplication/division third, and addition/subtraction fourth.

• In Python, spaces after a number or symbol do not carry any meaning. So, 5**3 and 5 ** 3 both result in 125.
• Spaces are meant to enhance readability. Although there is no correct way to space code, spaces are generally encouraged between operands and operators.
• Thus, 5 ** 3 is preferable.

• Python is completely object oriented, and not "statically typed". You do not need to declare variables before using them, or declare their type. Every variable in Python is an object.
• Python variables are dynamically typed. Meaning ,they get a datatype during the runtime depending on the value they are assigned with.
• The following code snippet shows the dynamic data type allocation in action.

C:\Users\ragha\.jupyter {git}{hg}
{lamb} python
Python 3.8.0 (tags/v3.8.0:fa919fd, Oct 14 2019, 19:37:50) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> y = 10
>>> type(y)
<class 'int'>
>>> y =  y - 10.0
>>> y
0.0
>>> type (y)
<class 'float'>
>>>

• Reassigning variables in terms of themselves. Use += shorthand operator to assign the value of the variable to itself after the operation being performed (here it is an addition). Example: x += 1 is equivalent to x = x + 1.
• Variable naming convention is recommended to have an indicative of their meaning/purpose like name,age etc., than just a short form of x, y etc.,
• There are a few restrictions on the naming conventions. A variable in Python cannot start with numbers, most special characters, keywords, or built-in types. Variables also can't contain spaces in between if it has more than one word. Example: my name is not a valid name, rather it can be given as my_name.
• According to Python conventions, it's best to use lowercase letters and to avoid special characters altogether as they will often cause errors.

• Python has a special way or an easy shortcut to let you assign the initial values to more than one variable in the same line, which is a terse, easy syntax, as follows.

x, y = 5, 8

• The above example assings the value 5 to the variable x and the value 8to the variabley`` respectively.
• It is also called as Pythonic way. Pythonic is a term used to describe code written in the optimum readable format.

• Keywords are the reserved words that have a special meaning to the compiler and they can't be used for the other/normal variables in a Python program/script. For exaample, int is a special word (reserved word or a keyword) that indicates that the variable following will have a numeral value associated with it.
• To get to know the list of keywords in the currently running version of python, you can use the following code snippet.Note: keyword is a module (a different pacckage that contains the variable kwlist) and it is not by default (naturally) available in your current Python script. Hence, it needs to be expliciltly made available (hence the name import) via the keyword import.

import keyword
print (keyword.kwlist)

You get the following output.

['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

• Comments are extra block of codes that do NOT run. They are meant to clarify the code for the readers.
• In Python, any text following by a pound/hash symbol (#) on a single line is considered as a comment.
• The comment can be either inline (as part of the executable statement - in the middle) or at the beginning of the line.
• The characters if any present after the # symbol are ignored and not executed.
• Example:

# This is a comment
# the below statement assigns the value 5 to the variable x
x = 5

pi = 3.14 # the value 3.14 is assigned to the variable pi, and this is an inline comment

• As a best practice, it is very well recommended to make an appropriate comment throughout your program to make the code legible to others.

• Docstrings, short for document strings, state what a given document, such as a program, a function, or a class, actually does. The primary difference in syntax between a docstring and a comment is that docstrings are intended to be written over multiple lines, which can be accomplished with triple quotes. They also introduce a given document, so they are placed at the top.
• Here is an example of a docstring:

"""
This document will explore why comments are particularly useful when writing and reading code.
"""

• When you execute this cell, nothing really happens. Docstrings, like comments, are designed as information for developers reading and writing code; they have nothing to do with the output of code.

• 8 and 8.0 - is equivalent in Mathematics (represent the same value but in different types) but not in Programming languages like Python.
• Integer - a whole number both positive and negative, including zero (0). Represented as int. Examples: 3, -2, 0 and 1000.
• Float - rational numbers expessed as fractions (decimal point). Represented as float. Example: 3.0, -2.0, 47.45 and 200.001.
• Python types can be obtained explicitly by using type() with a value inside it as a parameter. Example: type(10) gives int.
• Any mathematical operations on {int, float} (example: int + flat) gives a float, otherwise the information/data will be lost. When possible, Python converts types to preserve information. Example : 5 + 3.14 gives 8.14 and NOT 8.
• Conversion: The datatype / value can be converted from one to another using an appropriate method whose name bears the datatype. Example: int(7.99999) gives the floating value as an integer as 7. Similarly, float(6) gives back 6.0.

• In Python, anything that goes between 'single' or "double" quotes is considered a string.

• Strings are commonly used to express words, but they have many other uses, including displaying information to the user and retrieving information from a user.

• Although strings may use single or double quotes, a given string must be internally consistent. That is, if a string starts with a single quote, it must end with a single quote. The same is true of double quotes.

• Python uses the backslash character, , called an escape sequence in strings, to allow for the insertion of any type of quote inside of strings. The character that follows the backslash in an escape sequence may be interpreted as mentioned in Python's official documentation, which follows. Of particular note is \n, which is used to create a new line.

• Escape Sequence Characters

  Escape Sequence	Meaning
  \newline	Ignored
  \\	Backslash()
  '	Single Quote (')
  "	Double Quote (")
  \n	ASCII Linefeed (LF)
  \r	ASCII Carriage Return
  \t	ASCII Horizontal Tab
  \v	ASCII Vertical Tab

• The multiplication and addition operators work with strings as well.

• In particular, the + operator combines two strings into one and is referred to as string concatenation

• The * operator, for multiplication, repeats a string.

• String or Variable Interpolation is possible through the new f formatting specifier in Python3.
• Python 3.6 added new string interpolation method called literal string interpolation and introduced a new literal prefix f. This new way of formatting strings is powerful and easy to use. It provides access to embedded Python expressions inside string constants.
• Example:

  name = 'World'
  program = 'Python'
  print(f'Hello {name}! This is {program}')
  

• Output :

   Hello World! This is Python
  

• Python scripts at times have an error on the console while running the scripts stating that Incosistent use of tabs and spaces in indentaion. For which an easy waay to use a tool called autopep8 which is an utility to be installed separately using the pip.
• Command to use autopep8 -i <python_script.py>
• Example:

  C:\rags\TechNotes\pythonNotes\samplePgms\util (master)
  ¿ autopep8 -i employee_password_encrypt.py
  
  C:\rags\TechNotes\pythonNotes\samplePgms\util (master)
  ¿
  

• Command to install the autopep8 is : pip install --upgrade autopep8