(python learn) 1 python environment

By default linux have python installed. There are two kind of enviroment in python. One is interactive enviroment. Like shell.  The other one is file enviroment. Like other programming languages， you put the code in a file and run it.

The interactive environment

input python you will get into the python interactive enviroment

[root@racnode1 test]# python
Python 2.6.6 (r266:84292, Dec  7 2011, 20:48:22)
[GCC 4.4.6 20110731 (Red Hat 4.4.6-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 8
8
>>> 1+1
2
>>> exit()

　　

The file evironment

There are three kind of python files.

source code　　-- with extension name ".py".  You can run this file without comiple it. Because the python interpreter will interpret and run it.

compiled code　-- with extension name ".pyc". You can compile a source code to generate a ".pyc" file. The compile methold is like below

import py_compile
py_compile.compile("1.py")

optimized code　-- with extension name ".pyo".  This is the code being optimized by python. You can generate the ".pyo" file in this way. 

pyton -O -m py_compile example.py 

　　

let`s create a source code and run it. to create a souce code python file you can use vi.

#!/usr/bin/python
print "hello world"

without the line # !/usr/bin/python, you will have to run the file in below way. 

[root@racnode1 test]# python test.py
hello world

with the line  # !/usr/bin/python, you can grant execution privilege to the file and run  

[root@racnode1 test]# chmod u+x test.py
[root@racnode1 test]# ./test.py
hello world
[root@racnode1 test]#

once we have source code, we can generate a compiled file ".pyc".

first you need to create another python file with below content.

[root@racnode1 test]# cat compile.py
import py_compile
py_compile.compile("test.py")

then run this file you will compile the "test.py"

[root@racnode1 test]# python compile.py
[root@racnode1 test]# ls
compile.py  test.py  test.pyc
[root@racnode1 test]# python test.pyc
hello world

then let`s see antother example for generating a ".pyo" file

[root@racnode1 test]# ls
compile.py  test.py  test.pyc  test.pyo
[root@racnode1 test]# python -O -m py_compile test.py
[root@racnode1 test]# python test.pyo
hello world

with the commind python -O -m py_compile  you will get an optimized py file.