Python in a Nutshell, 2nd Edition

Running Other Programs

You can run other programs via functions in the os module or, in Python 2.4, by using the new subprocess module.

Running Other Programs with the os Module

In Python 2.4, the best way for your program to run other processes is with the new subprocess module, covered in The Subprocess Module. However, the os module also offers several ways to do this, which in some cases may be simpler or allow your code to remain backward-compatible to older versions of Python.

The simplest way to run another program is through function os.system, although this offers no way to control the external program. The os module also provides a number of functions whose names start with exec. These functions offer fine-grained control. A program run by one of the exec functions replaces the current program (i.e., the Python interpreter) in the same process. In practice, therefore, you use the exec functions mostly on platforms that let a process duplicate itself by fork (i.e., Unix-like platforms). os functions whose names start with spawn and popen offer intermediate simplicity and power: they are cross-platform and not quite as simple as system, but simple and usable enough for most purposes.

The exec and spawn functions run a specified executable file, given the executable file’s path, arguments to pass to it, and optionally an environment mapping. The system and popen functions execute a command, which is a string passed to a new instance of the platform’s default shell (typically ...