Python in a Nutshell

Running Other Programs

The os module offers several ways for your program to run other programs. 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, however, 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). Finally, 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, a string passed to a new instance of the platform’s default shell (typically /bin/sh on Unix, command.com or cmd.exe on Windows). A command is a more general concept than an executable file, as it can include shell functionality (pipes, redirection, built-in shell commands) using the normal shell syntax specific to the current platform.