reload a python file after making an edit without restarting the repl

reloader.py

"""
Drop in REPL: `import reloader; reloader.interact()` at the bottom of a script.

Gives you tab completion, persistent history and reload() function
that re-execs the calling-scropt into the live REPL namespace
"""

import atexit
import code
import os
import readline
import rlcompleter
import sys

def interact(ns=None, histfile=None, banner=""):
  if ns is None:
    # the globals of whoever called uss, i.e the script's namespace
    ns = sys._getframe(1).f_globals

  # reload() re-execs the caller, which calls interact() again- bail out
  if ns.get("_RELOADER_ACTIVE"):
    return
  ns["_RELOADER_ACTIVE"] = True

  src_file = ns.get("__file__")

  if histfile is None:
    # per script history, eg: ~/.file.py.history
    name = os.path.basename(src_file) if src_file else "repl"
    histfile = os.path.expanduser(f"~/.{name}.history")

  def reload():
    """re-exec the calling script into the REPL's namespace"""
    with open(src_file) as f:
      exec(compile(f.read(), src_file, "exec"), ns)
    print(f"reloaded {src_file}")

  ns["reload"] = reload

  try:
    readline.read_history_file(histfile)
  except OSError:
    pass

  readline.set_history_length(1000)
  atexit.register(readline.write_history_file, histfile)

  readline.set_completer(rlcompleter.Completer(ns).complete)

  if "libedit" in (readline.__doc__ or ""):
    readline.parse_and_bind("bind ^I rl_complete") # macOS system libedit
  else:
    readline.parse_and_bind("tab: complete")

  code.interact(local=ns, banner=banner)

Where to place this?

mkdir -p "$(python3 -m site --user-site)"
cp reloader.py $(python3 -m site --user-site)