Regrettably I cannot submit a PR for the docs because I value my online anonymity and Python submissions require a real name (IIRC), but my suggestion would be pretty simple.

Taking as an example, for termios (https://docs.python.org/3/library/termios.html), we currently have:

This module provides an interface to the POSIX calls for tty I/O control. For a complete description of these calls, see termios(3) Unix manual page. It is only available for those Unix versions that support POSIX termios style tty I/O control configured during installation.


For readline (https://docs.python.org/3/library/readline.html#module-readline) we have:

The readline module defines a number of functions to facilitate completion and reading/writing of history files from the Python interpreter. This module can be used directly, or via the rlcompleter module, which supports completion of Python identifiers at the interactive prompt. Settings made using this module affect the behaviour of both the interpreter’s interactive prompt and the prompts offered by the built-in input() function.

In similar way to the first para of the termios description I would add the following text:  “It is only available on platforms that support the readline functionality, generally POSIX”.


Then perhaps I’d also add to the cmd documentation at https://docs.python.org/3/library/cmd.html

The Cmd class provides a simple framework for writing line-oriented command interpreters. These are often useful for test harnesses, administrative tools, and prototypes that will later be wrapped in a more sophisticated interface.

I would add at the end of that first paragraph:
“Some features will be unavailable on non-POSIX platforms due to the readline requirement”.

Hope this helps, if it's not clear I can provide in diff form if you prefer.