cmd module tab-complete is broken

[bkad]

I'm unable to get tab-completion to work on the built-in cmd module using the following steps:

1. Using either the standalone build, run python3 -c 'import cmd; cmd.Cmd().cmdloop()'.
2. Try to tab-complete the "help" command. It fails on my machines using the standalone build, but works using my installation from brew.

I've tested this on the following, although it's possibly broken on all of them:

• macOS x86
• macOS ARM
• linux x86v2

Tab-completion works just fine in the standalone build's standard python REPL. Setting TERMINFO_DIRS=/usr/share/terminfo doesn't seem to help.

[bkad]

Think this is due to readline being compiled against libedit instead of GNU readline. If you override the default cmdloop implementation with one compatible with libedit, it seems to work just fine.

import cmd
import readline

class MyPrompt(cmd.Cmd):
    def cmdloop(self, intro=None):
        self.preloop()
        self.old_completer = readline.get_completer()
        readline.set_completer(self.complete)

        # use the libedit incantation rather than GNU readline
        readline.parse_and_bind("bind ^I rl_complete")

        try:
            if intro is not None:
                self.intro = intro
            if self.intro:
                self.stdout.write(str(self.intro) + "\n")
            stop = None
            while not stop:
                if self.cmdqueue:
                    line = self.cmdqueue.pop(0)
                else:
                    if self.use_rawinput:
                        try:
                            line = input(self.prompt)
                        except EOFError:
                            line = "EOF"
                    else:
                        self.stdout.write(self.prompt)
                        self.stdout.flush()
                        line = self.stdin.readline()
                        if not len(line):
                            line = "EOF"
                        else:
                            line = line.rstrip("\r\n")
                line = self.precmd(line)
                stop = self.onecmd(line)
                stop = self.postcmd(stop, line)
            self.postloop()
        finally:
            readline.set_completer(self.old_completer)

if __name__ == '__main__':
    MyPrompt().cmdloop()

[bkad]

I'm convinced now that this is an issue with python's implementation of the cmd module and not with this project.