commandwrapper

commandwrapper is a Python module to wrap a shell command into a Python threaded object.

Usage:

You want to launch the following bash commands in a thread:

[user@localhost ~]$ ls -l | grep pdf | wc -l
5

here is how you can do it:

>>> Ls = WrapCommand( 'ls -l')
>>> GrepPdf = WrapCommand( 'grep pdf')
>>> Wc = WrapCommand( 'wc -l')
>>> Wc.stdin = GrepPdf
>>> GrepPdf.stdin = Ls
>>> Wc.start( )
>>> #Do stuff
...
>>> Wc.join()
>>> Wc.results
('5\n', '')

the 'results' property is a tuple (stdoutdata, stderrdata)

You can also do it this way:

>>> Ls = WrapCommand( 'ls -l | grep pdf | wc -l', shell=True)
>>> Ls.start()
>>> #Do stuff
>>> Ls.join()
>>> Ls.results[0]
'5\n'

You would need to specify 'shell=True' when the command you wish to execute is actually built into the shell. i.e.: on Windows if you use built in commands such as 'dir' or 'copy': http://docs.python.org/library/subprocess.html#subprocess.Popen

The purpose of doing it in a thread is when the above commands may take a few hours, and that you want to perform other tasks in the meanwhile. You can check the process is still running with:

>>> Wc.is_alive( )
False

'True' would be returned if still running. To terminate it prematurely (i.e. it deadlocked) you have the 'terminate()', 'kill()' or 'send_signal(signal) methods which are self speaking. When you want to wait for the thread to end, use the 'join()' method: http://docs.python.org/library/threading.html#threading.Thread.join

You want to launch the following bash commands without threading:

[user@localhost ~]$ ls -l | grep pdf | wc -l
5

here is how you can do it:

>>> Ls = WrapCommand( 'ls -l')
>>> GrepPdf = WrapCommand( 'grep pdf')
>>> Wc = WrapCommand( 'wc -l')
>>> Wc(GrepPdf(Ls))
'5\n'

Avoid doing this for processes where a large amount of data is piped between each command.

instead, do it this way:

>>> Ls = WrapCommand( 'ls -l | grep pdf | wc -l', shell=True)
>>> Ls()
'5\n'

Prefer the threaded method instead if this may take a long time and that you want to perform other tasks in the meanwhile.

You can specify another shell for running commands:

>>> Ls = WrapCommand( 'ls', shell=True, executable='C:/windows/System32/WindowsPowerShell/v1.0/powershell.exe')
>>> print Ls()

 Directory : C:\Users\Yves\python_tests

Mode LastWriteTime Length Name
---- ------------- ------ ----
-a--- 27/01/2011 00:14 7006 commandwrapper.py
-a--- 27/01/2011 00:15 7048 commandwrapper.pyc

You can also use Context Management (with_item): http://docs.python.org/reference/compound_stmts.html#grammar-token-with_item

example:

>>> with WrapCommand( 'ls -l') as Ls:
... with WrapCommand( 'grep pdf') as GrepPdf:
... with WrapCommand( 'wc -l') as Wc:
... Wc.stdin = GrepPdf
... GrepPdf.stdin = Ls
... Wc.start( )
... #Do stuff
... Wc.join()
...
>>> Wc.results
('5\n', '')

You may also simply want to have a subprocess objet:

>>> ls = WrapCommand( 'ls -l')
>>> lscmd = ls.makeCmd()
>>>

the returned object (lscmd in the example above) is a standard subprocess.Popen object

WrapOnceCommand is the same as WrapCommand, but the cmd attribute which is a subprocess.Popen object will be created once and for all Therefore the run methode (or the object) can only be called once. The goal it to launch a command in a thread, and to have this command easily start/stopped from elsewhere.

What is new in this release:

• Changed author's contact info.

What is new in version 0.4:

• The Warning here: http://docs.python.org/reference/datamodel.html#object.__del__
• And becasue destroyed objects where not automaticaly removed by the garbage collector as described here: http://docs.python.org/library/gc.html#gc.garbage Which could cause memory usage increase.

Requirements:

• Python