cs.x 20170902

X(), for low level debugging

X() is my function for low level ad hoc debug messages. It takes a message and optional format arguments for use with %. It is presented here in its own module for reuse.

It normally writes directly to sys.stderr but accepts an optional keyword argument file to specify a different filelike object.

Its behaviour may be tweaked with the globals X_logger or X_via_tty. If file is not None, write to it unconditionally. Otherwise, if X_logger then log a warning to that logger. Otherwise, if X_via_tty then open /dev/tty and write the message to it. Otherwise, write the message to sys.stderr.