Subclasses: Another redeeming part of OOP. Another redeeming part of OOP. Generally, I do not "get" OOP. Objects have one good use in my book: they make convenient namespaces. 90% of the time I see people using a million objects where they are not really needed, solely because OOP lets you waste time writing a skeleton when you otherwise have no clue what to do. But today I found a second redeeming quality to objects. Used sparingly, subclasses make great self documentation. I've been working on a project with some peculiar communications requirements. ... and of course there are a lot of other event handlers to write (each parses an event into a message). How do you make this core interface clear? When it doubt, use more layers. And that is one way to document through subclassing. SocketServer: Now with a complete example. -> Bonus: simple python socket client. February 2009: Now with a complete example.
April 2009: Bonus: simple python socket client Python 2.6 and 3.0 introduced a lot of new modules. Here I'll be covering one of them, SocketServer, which provides a dead easy way to build custom servers. We'll be implementing a port-to-pipe adapter. Anything that comes in to a network port will be passed through the standard input pipe to an application. The application's output will be collected and routed back through the network port. What's good will this example be? We'll be creating a network enabled calculator. First, accessing the command line from Python.
Def pipe_command(arg_list, standard_input=False): "arg_list is [command, arg1, ...], standard_input is string" pipe = subprocess.PIPE if standard_input else None subp = subprocess.Popen(arg_list, stdin=pipe, stdout=subprocess.PIPE) if not standard_input: return subp.communicate()[0] return subp.communicate(standard_input)[0] Finally, everything is set up. . $ nc localhost 2000 2+2 4 #! Zaur Nasibov's Inside Python subprocess communication. Sometimes, it’s really hard to understand what happens inside a function or even a whole module of Python’s Standard library.
For example, the subprocess module contains a very tricky Popep class. I tried to use the the module to communicate with a MATLAB subprocess shell (e.g. send MATLAB commands to subprocess and read the output). Unfortunately I failed and was just able to pass a MATLAB script via command-line arguments. Yet, I learnt much about the Popen.communicate() method and I’d like to share this knowledge with you. Before we begin I love Python and try using the latest versions when possible. . # XXX Rewrite these to use non-blocking I/O on the# file objects; they are no longer using C stdio!
Then, there is a pending Asynchronous I/O For subprocess. Temporary moratorium (suspension) of all changes to the Python language syntax, semantics, and built-ins for a period of at least two years from the release of Python 3.1 was proposed and accepted in PEP 3003. A simple experiment. Subprocess – Work with additional processes. The subprocess module provides a consistent interface to creating and working with additional processes. It offers a higher-level interface than some of the other available modules, and is intended to replace functions such as os.system(), os.spawn*(), os.popen*(), popen2.*() and commands.*().
To make it easier to compare subprocess with those other modules, many of the examples here re-create the ones used for os and popen. The subprocess module defines one class, Popen and a few wrapper functions that use that class. The constructor for Popen takes arguments to set up the new process so the parent can communicate with it via pipes. It provides all of the functionality of the other modules and functions it replaces, and more. Note The API is roughly the same, but the underlying implementation is slightly different between Unix and Windows. Running External Command To run an external command without interacting with it, such as one would do with os.system(), Use the call() function. popen. Python - subprocess with timeout.