Return an open file object connected to the file descriptor fd.
The mode and bufsize arguments have the same meaning as
the corresponding arguments to the built-in open()
function.
Availability: Macintosh, Unix, Windows.
Open a pipe to or from command. The return value is an open
file object connected to the pipe, which can be read or written
depending on whether mode is 'r' (default) or 'w'.
The bufsize argument has the same meaning as the corresponding
argument to the built-in open() function. The exit status of
the command (encoded in the format specified for wait()) is
available as the return value of the close() method of the file
object, except that when the exit status is zero (termination without
errors), None is returned.
Availability: Unix, Windows.
