simple import hook for renaming modules

renamehook.py

from importlib import import_module
from sys import modules
from warnings import warn
from datetime import date, timedelta
from collections import namedtuple

class RenameHook:
    def __init__(self, registry):
        self.registry = registry

    def find_module(self, fullname, path=None):
        if fullname in self.registry:
            entry = self.registry[fullname]
            if len(entry) == 4:
                warning_date, exception_date, new_name, old_name = entry
            else:
                warning_date = date.today()
                exception_date = date.today() + timedelta(1)
                new_name = entry

            msg = ' '.join(['{} has been moved to {} as of {:%Y-%m-%d};',
                            'it will no longer be available after {:%Y-%m-%d}',
                            'please update your imports'])
            msg = msg.format(fullname, new_name, warning_date, exception_date)
            if date.today() >= exception_date:
                raise ImportError(msg)
            elif date.today() >= warning_date:
                warn(msg, DeprecationWarning)
                return self

    def load_module(self, fullname):
        entry = self.registry[fullname]
        if len(entry) == 4:
            new_name = entry.new_name
        else:
            new_name = entry
        mod = import_module(new_name)
        modules[fullname] = mod
        return mod

RenamedModule = namedtuple('RenamedModule', 'from_date to_date new_name old_name')

if __name__ != '__main__':
    registry = {'moth':   RenamedModule(date(2015, 4, 1), date(2016, 4, 1),
                                        'math', 'moth'),
                'random': 'numpy.random',
                'linalg': 'numpy.linalg' }

    import sys
    sys.meta_path = [RenameHook(registry)] + sys.meta_path