Python program execution process, Byte code, Python Virtual Machine, Create .pyc file, Display .pyc file, Flavours of Python - CPython, IronPython, Jython, PyPy.

1. PYTHON INTRODUCTION

2. Program Execution
 Step 1: Create source code
 Write a Python program through Python IDLE or any text editor
and save the program with ‘.py’ file extension.
 Step 2: Run source code
 We can run Python source code in two ways:
 1. Through Python IDLE
 2. Through system command prompt

3. Program Execution
 Through Python IDLE:
 Open your source code file in IDLE
 Click ‘Run’ menu, select ‘Run module’ command or press
‘F5’

4. Program Execution
 Through system command prompt:
 Open system command prompt.
 Change current directory to Python local directory.
 Use ‘python’ command with source code file name.
F:PYTHON>python if.py
Enter first value::
34
Enter second value::
67
Addition = 101

5. Program Execution
Python Compiler
Source code
sum.py
Byte code
sum.pyc
Python Virtual Machine
Python Interpreter
Machine code
Processor
Output
Enter first value::
34
Enter second value::
67
Addition = 101

6. Byte Code
 Python compiler generate byte code file from source code.
 Extension of byte code file is ‘.pyc’.
 Byte code file store a set of fixed length instructions.
 Length of each instruction is 1 byte.
 These instructions represent all operations like arithmetical,
comparison, memory related etc.
 Byte code is platform independent.

7. Python Virtual Machine
 Main role of PVM is convert byte code to machine code.
 PVM contain an interpreter, which make this conversion.
 Machine code is machine specific.
 Machine code directly executes through processor.

8. Create ‘.pyc’ File
 Use following command to create ‘.pyc’ file:
 In above command we call Python compiler through
‘python’ command with ‘-m’ option.
 ‘-m’ option represent module and module name is
‘py_compile’.
 All ‘.pyc’ file store in ‘__pycache__’ folder.
F:PYTHON>python -m py_compile source_code_file

9. Create ‘.pyc’ File
 We can run ‘.pyc’ file directly
F:PYTHON>python __pycache__if.cpython-37.pyc
Enter first value::
23
Enter second value::
45
Addition = 68

10. Display ‘.pyc’ File
 To display contain of ‘.pyc’ file use following command:
 Here we use ‘dis’ module to display byte code in human
readable format.
 ‘dis’ module is also known as ‘disassembler’.
F:PYTHON>python -m dis if.py

11. Flavours Of Python
 Cpython:
 This compiler implemented in C language.
 Here source code converted into bytecode through
some functions written in C language.
 PVM interpreter also implemented in C language.
 In Cpython we can run C or C++ program.

12. Flavours Of Python
 Jython:
 This Python flavour design to run Python program on
Java Virtual Machine.
 The compiler generate Java byte code from Python
source code, which run in JVM.
 Jython libraries useful for both Java and Python.

13. Flavours Of Python
 Iron Python:
 This Python flavour implemented for Microsoft .net
framework.
 Its compiler written in C# language.
 This compiler generate an intermediate language from
Python source code, which run on Common Language
Runtime ( CLR ).

14. Flavours Of Python
 PyPy:
 This Python compiler implemented by RPython
language.
 PyPy programs run very fast, because its added ‘Just In
Time’ ( JIT ) compiler in PVM instead of interpreter.