Python script to implement bash completion (tested only on Ubuntu 18.04 and python 3.8).

complete.py

"""
Example:
    python3 complete.py define my_command
        - Define this script as the handler in .bashrc
        - Note: this will overwrite any previous handler

    python3 complete.py undef my_command
        - Remove it from .bashrc

    python3 complete.py complete <current_word> <full_line>
        - current_word is the index (starting with 1) of the word
        - full_line is the full line, in a single argument
        - This will print all the matching words on the standard output

Note:
- The header and footer should not be altered in any way

"""

import os
import shlex

'''
Variables containing COMP_ accessible when inside the completion function (
    I might have forgot some variables that does not contain COMP_)
Those are not used in this script (except the COMP_CWORD and COMP_LINE), because
    I either didn't find a use for them or I can't find their definition.
BASH_COMPLETION_VERSINFO=([0]="2" [1]="8")
COMP_CWORD=5
COMP_KEY=9
COMP_LINE='none  ed '\'' est  hi hi hi '\''h'\''  hd  '\''   test "hi" '
COMP_POINT=48
COMP_TYPE=63
COMP_WORDBREAKS=' 	
COMP_WORDS=([0]="none" [1]="ed" [2]="' est  hi hi hi 'h'  hd  '" [3]="test" [4]="\"hi\"" [5]="")
'''


def complete(current_word, full_line):
    split = shlex.split(full_line)
    return list(i for i in list(i + "-level-" + current_word for i in ("test", "test-中文", 'test-한글')) if i.startswith(
        "" if len(split) - 1 < int(current_word) else split.__getitem__(int(current_word))))


if __name__ == '__main__':
    command = os.sys.argv.__getitem__(1)
    if command in ('define', 'undef'):
        definition = command == 'define'
        alias = os.sys.argv.__getitem__(2)
        "The next line is to make sure the command does not contain"
        "   strange characters or spaces"
        assert shlex.quote(alias) == alias, (alias, shlex.quote(alias))
        command_name = '__auto_complete_' + alias + '_function'
        header = '# >>> ' + 'autocomplete definition of ' + alias + ' >>>'
        footer = '# <<< ' + 'autocomplete definition of ' + alias + ' <<<'
        if definition:
            bash_script = f'''
{command_name} () {{
    COMPREPLY=($({shlex.join((os.sys.executable, os.sys.argv.__getitem__(0)))} complete $COMP_CWORD "${{COMP_LINE}}"));
}};'''
            aliasing = 'complete -F ' + command_name + ' ' + alias
            warning = '# !!! Content defined withing this block is' \
                      ' auto generated and might be deleted !!!'
            content = '\n'.join((header, warning, bash_script, aliasing, footer))
        else:
            content = ''
        bashrc_path = os.path.expanduser('~/.bashrc')
        bashrc = open(bashrc_path).read()

        def write_and_refresh(new_content: str):
            while not new_content.endswith('\n'*3):
                new_content += '\n'
            os.rename(bashrc_path, bashrc_path + '.bak')
            open(bashrc_path, 'x').write(new_content)
            "subprocess.Popen(list(('source', bashrc_path)), shell=True).wait()"

        try:
            index = bashrc.index(header)
        except ValueError:
            try:
                footer_index = bashrc.index(footer)
            except ValueError:
                if definition:
                    write_and_refresh(bashrc.rstrip() + '\n'*3 + content + '\n'*3)
                else:
                    raise NameError('%r was not found' % (alias, ))
            else:
                raise RuntimeError('Corrupted bashrc: footer but no header')
        else:
            try:
                footer_index = bashrc.index(footer)
            except ValueError:
                raise RuntimeError('Corrupted bashrc: header but no footer')
            else:
                old_content = bashrc.__getitem__(slice(index, footer_index + len(footer))).strip()
                if old_content != content:
                    assert bashrc.count(old_content) == 1, 'This should not be happening'
                    write_and_refresh(bashrc.replace(old_content, content).rstrip())
    elif command == 'complete':
        os.sys.stdout.write(' '.join(complete(
            *os.sys.argv.__getitem__(slice(2, None)))))
        os.sys.stdout.flush()
    else:
        raise NotImplementedError(command)