# Understanding the Execution of Python Program


<!--more-->

## Python

* A kind of script language, interpret at the execution rather than compiling.

* Application

  * web development

  * scientific computation

  * machine learning

## What would Happen When We Execute the Python Source File. 

The actions after `python <SOURCE_FILE>.py`

  * CPython(Interpreter) would first translate our source file into the byte codes.

  * The translated byte code would cache in `__pycache__` directory and named with `.pyc` suffix.

  * After translated to the byte code, the byte code could be executed on the `PVM(Python Virtual Machine)`.

## JIT(Just In Time Compile)

Due to the byte code instructions execute on the virtual machine is not the behavior on our processor in physically, so 
here's why JIT comes out.

  * Analyzing the byte code at run-time and compile to the machine code that our processor can read directly.

  * The machine code is optimized according to our run-time behavior.

## Comparing Interpreter and Compiler

|                    | Interpreter | Compiler |
| ------------------ | ----------- | -------- |
| Run Time Execution | Slow        | Fast     |
| Debug              | Easy        | Annoying |