preexec_fn is supplied, it will be called with no arguments in the
        child process before exec-ing the specified command.
        It may, for instance, set signal handlers to SIG_DFL or SIG_IGN.

        Dimensions of the psuedoterminal used for the subprocess can be
        specified as a tuple (rows, cols), or the default (24, 80) will be used.
        z)Expected a list or tuple for argv, got %rNr