Remote neovim command that changes the selected range (python)

Question

I want a simple command that changes the range that the user selected to a constant string I set (with possibly differently number of lines) - effectively adding lines if the constant string has more. The following code does nothing but randomly inserts newline. What went wrong?

class Plugin(object):
    def __init__(self, nvim):
        self.nvim = nvim

    @neovim.command("MyCommand", range="", nargs="*", sync=True)
    def my_command(self, args, range):
        start_line, end_line = range
        region = self.nvim.current.buffer.range(start_line-1, end_line)
        aa="string \r ssss"  
        if len(aa)>0:
            region[:] = '\r'.split(aa)

Answer 1

I would add a file: nvim\rplugin\python3\mycommand.py to the nvim configuration.

With the following content:

import pynvim

@pynvim.plugin
class Plugin(object):
    def __init__(self, nvim):
        self.nvim = nvim

    @pynvim.command("MyCommand", range="", nargs=0, sync=True)
    def my_command(self, args, rgn):
        start_line, end_line = rgn
        self.nvim.command(f"echo {start_line} {end_line}")

        text="alpha\rbeta\rgamma"
        lines = text.split("\r")

        if len(lines) < end_line + 1 - start_line:
            # Remove lines in excess:
            self.nvim.call("deletebufline", "%", start_line + len(lines), end_line)

        for i in range(len(lines) - (end_line + 1 - start_line)):
            # Insert missing blank lines:
            self.nvim.call("appendbufline", "%", end_line, "")

        for index, line in enumerate(lines):
            # Replace lines with the text:
            self.nvim.call("setbufline", "%", start_line + index, line)

It assumes that pynvim package is available in the Python version that Neovim is using (defined in g:python3_host_prog)