The readline module defines a number of functions used either
directly or from the rlcompleter module to facilitate
completion and history file read and write from the Python
interpreter.
The readline module defines the following functions:
Set the number of lines to save in the history file.
write_history_file() uses this value to truncate the
history file when saving. Negative values imply unlimited history
file size.
Set or remove the completer function. The completer function is
called as function(text, state),
for i in [0, 1, 2, ...] until it returns a non-string.
It should return the next possible completion starting with text.