Monday 29 April 2019

2. Coding Introduction

2.   Python coding introduction   -     10 min read
  • Installing Python on Windows OS
  • Ways to write a python program
  • Python program execution steps
  • Understanding first python program
  • First python program executing by using python IDLE
  • Python program internal flow: Short answer
  • Python program internal flow: Long answer
  • Python Virtual Machine
  • JIT Compiler
  • Programs
2. Python coding introduction

2.1 Ways to write a python program
  • We can write the python programs in two ways.
    • By using any text editor like Notepad++, Edit plus.
    • We can also write python programs by using python IDLE(Integrated Development Environment)
2.2 Python program execution steps
  • We need to write python programs in notepad (good approach for practice).
  • We can save the program with .py or .python extension.
  • Run or execute the program.
  • Finally, we will get output.

Program       Print Welcome to python world message

print(“Welcome to python world”)               

Run             python
Run             py

Welcome to python world

2.7 Understanding first python program
  • print("Welcome to python world”),
    • print() is a predefined function.
    • print() function takes string values as parameters.
  • This function prints the output on the console.
2.6 Execute first Python program by python IDLE or command prompt
  • Open python IDLE
  • ü  Then write directly like, print(“Welcome to python world”)
>>>print (“Welcome to python world”)
Welcome to python world

2.3 Python program flow
Short answer
  • Python program (source code), we need to save with .py (dot py) or .python (dot python) extension.
    • Example      :
  • We can run this program by using python command.
    • While running the program, internally automatic compilation will be done.
    • If everything perfect as per compiler checking then goes to next level to execute the program.
    •  Example      :        python
  • We can see the output on the console.
2.3 Python program flow
  • Long answer but more helpful for internal understandings…
  • This answer mainly contains three parts,
    1. Write and Run the program
    2. Compiled python file
    3. Python Virtual machine
1. Write and run the program
  • Python program (source code), we need to save with .py (dot py) or .python (dot python) extension.
    • Example      :
  • Next step is, we need to run this program (
2. Compiled python file
  • While running the program, the first step is, internally python compiler takes this source code and creates corresponding compiled python file to the source code.
    • This compiled python file is not visible.
    • It is a hidden file, stored in cache memory.
    • If we want to see this file then run this below command,
    • python -m py_compile
  • -m means module here py_compile is module name.
  • This module creates a compiled python file.
  • So, python creates a separate folder in the current directory by the name _pycache_ to store compiled python file.
3. Python Virtual Machine
  • This compiled python file contains byte code instructions.
  • These byte code instructions are not understandable by the microprocessor to generate output.
  • While running the program, Python Virtual Machine takes responsible to convert these byte code instructions into machine understandable format
    •  Example      :        python
  • Finally, we will see the output
JIT compiler (Just In Time)
  • Python Virtual Machine internally uses interpreter which converts line by line, so it is very slow.
  • To resolve this problem few python flavours (PyPy) uses compiler which converts very faster than an interpreter.
  • This compiler is called JIT (Just In Time) compiler.
  • It improves the speed and execution of a python program