Introducing the os Modules

Tools in the os Modules

Table 2-1. Commonly used os module tools

Tasks	Tools
Shell variables	os.environ
Running programs	os.system, os.popen, os.execv, os.spawnv
Spawning processes	os.fork, os.pipe, os.waitpid, os.kill
Descriptor files, locks	os.open, os.read, os.write
File processing	os.remove, os.rename, os.mkfifo, os.mkdir, os.rmdir
Administrative tools	os.getcwd, os.chdir, os.chmod, os.getpid, os.listdir, os.access
Portability tools	os.sep, os.pathsep, os.curdir, os.path.split, os.path.join
Pathname tools	os.path.exists('path'), os.path.isdir('path'), os.path.getsize('path')

 

Administrative Tools

>>> os.getpid()
7980
>>> os.getcwd()
'C:\\PP4thEd\\Examples\\PP4E\\System'

>>> os.chdir(r'C:\Users')
>>> os.getcwd()
'C:\\Users'

 

Portability Constants

>>> os.pathsep, os.sep, os.pardir, os.curdir, os.linesep
(';', '\\', '..', '.', '\r\n')

 

Common os.path Tools

>>> os.path.isdir(r'C:\Users'), os.path.isfile(r'C:\Users')
(True, False)
>>> os.path.isdir(r'C:\config.sys'), os.path.isfile(r'C:\config.sys')
(False, True)
>>> os.path.isdir('nonesuch'), os.path.isfile('nonesuch')
(False, False)

>>> os.path.exists(r'c:\Users\Brian')
False
>>> os.path.exists(r'c:\Users\Default')
True
>>> os.path.getsize(r'C:\autoexec.bat')
24

>>> os.path.split(r'C:\temp\data.txt')
('C:\\temp', 'data.txt')

>>> os.path.join(r'C:\temp', 'output.txt')
'C:\\temp\\output.txt'

>>> name = r'C:\temp\data.txt'                            # Windows paths
>>> os.path.dirname(name), os.path.basename(name)
('C:\\temp', 'data.txt')

>>> name = '/home/lutz/temp/data.txt'                     # Unix-style paths
>>> os.path.dirname(name), os.path.basename(name)
('/home/lutz/temp', 'data.txt')

>>> os.path.splitext(r'C:\PP4thEd\Examples\PP4E\PyDemos.pyw')
('C:\\PP4thEd\\Examples\\PP4E\\PyDemos', '.pyw') 

 

Running Shell Commands from Script

Other os module Exports

Introducing the sys Module

Introducing the sys Modeule

Platforms and Versions

C:\...\PP4E\System> python
>>> import sys
>>> sys.platform, sys.maxsize, sys.version
('win32', 2147483647, '3.1.1 (r311:74483, Aug 17 2009, 17:02:12) ...more deleted...')

>>> if sys.platform[:3] == 'win': print('hello windows')
...
hello windows

 

The Module Search Path

>>> sys.path
['', 'C:\\PP4thEd\\Examples', ...plus standard library paths deleted... ]

>>> sys.path.append(r'C:\mydir')
>>> sys.path
['', 'C:\\PP4thEd\\Examples', ...more deleted..., 'C:\\mydir'] 

The Loaded Modules Table

>>> sys.modules
{'reprlib': <module 'reprlib' from 'c:\python31\lib\reprlib.py'>, ...more deleted...

>>> list(sys.modules.keys())
 ['reprlib', 'heapq', '__future__', 'sre_compile', '_collections', 'locale', '_sre',
'functools', 'encodings', 'site', 'operator', 'io', '__main__', ...more deleted... ]

>>> sys
<module 'sys' (built-in)>
>>> sys.modules['sys']
<module 'sys' (built-in)>

Exception Details

>>> import traceback, sys
>>> def grail(x):
...     raise TypeError('already got one')
...
>>> try:
...     grail('arthur')
... except:
...     exc_info = sys.exc_info()
...     print(exc_info[0])
...     print(exc_info[1])
...     traceback.print_tb(exc_info[2])
...
<class 'TypeError'>
already got one
  File "<stdin>", line 2, in <module>
  File "<stdin>", line 2, in grail

 

Programming Python

2 System Programming

• System scripting overview
• Intruducing sys Module
• Introducing os Module

System Scripting Overview

• dir, dir(sys), dir(os), dir(os.path)
• import, import sys, import os
• sys.__doc__, print(sys.__doc__)
• help(sys)
• >>> line = 'aaa\nbbb\nccc\n' >>> line.split('\n') ['aaa', 'bbb', 'ccc', ''] >>> line.splitlines() ['aaa', 'bbb', 'ccc']
• String Method Basics
• mystr.find('XXX'), >>> mystr.find('SPAM') # return first offset 3
• mystr.replace('AA', 'XXX'), >>> mystr.replace('aa', 'SPAM') # global replacement 'xxSPAMxxSPAM'
• 'XXX' in mystr, >>> 'SPAM' in mystr # substring search/test True

Step 2: Storing Record Persistently

To make our people persistent, they need to be stored in a file or some sort.

Using formatted files

One way to keep our data around between our program runs is to write all the data out to a simple text file, in a formatted way.

Data format script

Step 1: Representing Data

Step 1: Representing Data


Using Lists
A database list
Field labels

Using Dictionaries
Other ways to make dictionaries
Lists of dictionaries
Nested Structures
Dictionaries of dictionaries


dict()

Programming Python

The task
You need track the information of people.
You want write programs that keeps track of details about people.

Step 1: Representing record
What records in a data base look like?

built-in objects: lists, dictionaries


Step 2: Storing Records Persistently
They need to be stored to file or some sort.


Step 3: Stepping up OOP
Structure, encapsulation and customization.


Step 4:  Adding Console Interaction


Step 5: Adding GUI


Step 6: Adding Web Interface
Basic CGI script