The popen2 module is used to spawn processes and connect to their input/output/error streams using pipes on UNIX and Windows. Note that these functions are also available in the os module with slightly different return values.
popen2(cmd [, bufsize [, mode]])
Executes cmd as a subprocess and returns a pair of file objects (child_stdout, child_stdin) corresponding to the input and output streams of the subprocess. bufsize specifies the buffer size for the I/O pipes. mode is one of 't' or 'b' to indicate text or binary data, which is needed on Windows.
popen3(cmd [, bufsize [, mode]])
Executes cmd as a subprocess like popen2(), but returns a triple (child_stdout, child_stdin, child_stderr) that includes the standard error stream.