Standard Library

Note

Reference document for this section:

• The Python Standard Library documentation: http://docs.python.org/library/index.html
• Python Essential Reference, David Beazley, Addison-Wesley Professional

os module: operating system functionality

“A portable way of using operating system dependent functionality.”

Directory and file manipulation

Current directory:

>>> os.getcwd()
>>> '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source'

List a directory:

>>> os.listdir(os.curdir)
['.index.rst.swo',
 '.python_language.rst.swp',
 '.view_array.py.swp',
 '_static',
 '_templates',
 'basic_types.rst',
 'conf.py',
 'control_flow.rst',
 'debugging.rst',
 ...

Make a directory:

>>> os.mkdir('junkdir')
>>> 'junkdir' in os.listdir(os.curdir)
True

Rename the directory:

>>> os.rename('junkdir', 'foodir')

>>> 'junkdir' in os.listdir(os.curdir)
False

>>> 'foodir' in os.listdir(os.curdir)
True

>>> os.rmdir('foodir')

>>> 'foodir' in os.listdir(os.curdir)
False

Delete a file:

>>> fp = open('junk.txt', 'w')    # first create an empty file
>>> fp.close()

>>> 'junk.txt' in os.listdir(os.curdir)
True

>>> os.remove('junk.txt')

>>> 'junk.txt' in os.listdir(os.curdir)
False

os.path: path manipulations

os.path provides common operations on pathnames:

>>> fp = open('junk.txt', 'w')

>>> fp.close()

>>> a = os.path.abspath('junk.txt')

>>> a
    '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/junk.txt'

>>> os.path.split(a)
    ('/Users/cburns/src/scipy2009/scipy_2009_tutorial/source',
     'junk.txt')

>>> os.path.dirname(a)
    '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source'

>>> os.path.basename(a)
    'junk.txt'

>>> os.path.splitext(os.path.basename(a))
    ('junk', '.txt')

>>> os.path.exists('junk.txt')
    True

>>> os.path.isfile('junk.txt')
    True

>>> os.path.isdir('junk.txt')
    False

>>> os.path.expanduser('~/local')
    '/Users/cburns/local'

>>> os.path.join(os.path.expanduser('~'), 'local', 'bin')
    '/Users/cburns/local/bin'

Running an external command

>>> from subprocess import call
>>> call('chmod +x filename', shell=True)

shutil: high-level file operations

The shutil provides useful file operations:

• shutil.rmtree: Recursively delete a directory tree.
• shutil.move: Recursively move a file or directory to another location.
• shutil.copy: Copy files or directories.

glob: Pattern matching on files

The glob module provides convenient file pattern matching.

Find all files ending in .txt:

>>> from glob import glob

>>> glob('*.txt')
['holy_grail.txt', 'junk.txt', 'newfile.txt']

>>> glob('[hn]*.txt')
['holy_grail.txt', 'newfile.txt']

Note that by default the results aren’t sorted. If you want the output list sorted, use:

>>> sorted(glob('[hn]*.txt'))

Environment variables:

>>> import os

>>> os.environ.keys()
['_',
 'FSLDIR',
 'TERM_PROGRAM_VERSION',
 'FSLREMOTECALL',
 'USER',
 'HOME',
 'PATH',
 'PS1',
 'SHELL',
 'EDITOR',
 'WORKON_HOME',
 'PYTHONPATH',
 ...

>>> os.environ['PYTHONPATH']
'.:/Users/cburns/src/utils:/Users/cburns/src/nitools:
/Users/cburns/local/lib/python2.5/site-packages/:
/usr/local/lib/python2.5/site-packages/:
/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5'

>>> os.getenv('PYTHONPATH')
'.:/Users/cburns/src/utils:/Users/cburns/src/nitools:
/Users/cburns/local/lib/python2.5/site-packages/:
/usr/local/lib/python2.5/site-packages/:
/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5'

sys module: system-specific information

System-specific information related to the Python interpreter.

• Which version of python are you running and where is it installed:

  >>> sys.platform
  'darwin'
  
  >>> sys.version
  '2.5.2 (r252:60911, Feb 22 2008, 07:57:53) \n
  [GCC 4.0.1 (Apple Computer, Inc. build 5363)]'
  
  >>> sys.prefix
  '/Library/Frameworks/Python.framework/Versions/2.5'
  

• List of command line arguments passed to a Python script:

  >>> sys.argv
  ['/Users/cburns/local/bin/ipython']
  

sys.path is a list of strings that specifies the search path for modules. Initialized from PYTHONPATH:

>>> sys.path
['',
 '/Users/cburns/local/bin',
 '/Users/cburns/local/lib/python2.5/site-packages/grin-1.1-py2.5.egg',
 '/Users/cburns/local/lib/python2.5/site-packages/argparse-0.8.0-py2.5.egg',
 '/Users/cburns/local/lib/python2.5/site-packages/urwid-0.9.7.1-py2.5.egg',
 '/Users/cburns/local/lib/python2.5/site-packages/yolk-0.4.1-py2.5.egg',
 '/Users/cburns/local/lib/python2.5/site-packages/virtualenv-1.2-py2.5.egg',
 ...