Overriding stdlib http package

hook.py

import sys

from importlib import invalidate_caches
from importlib.abc import MetaPathFinder
from importlib.machinery import ModuleSpec, SourceFileLoader
from os.path import dirname, join, abspath, isdir, isfile


class Finder(MetaPathFinder):
    def find_spec(self, fullname, path, target=None):
        name_parts = fullname.split('.')
        if name_parts[0] != 'http':
            # don't worry about non-http modules
            return

        name_parts[0] = 'httplib3'
        find_path = abspath(join(*name_parts))

        if isdir(find_path):
            origin = join(find_path, '__init__.py')
        else:
            origin = '{}.py'.format(find_path)
            if not isfile(origin):
                # assume it's a module attribute
                return

        loader = SourceFileLoader(fullname, origin)
        is_package = loader.is_package(fullname)

        spec = ModuleSpec(
            fullname, loader, is_package=is_package, origin=origin)
        if is_package:
            spec.submodule_search_locations = [dirname(__file__)]

        return spec


def inject():
    invalidate_caches()
    for k in [k for k in sys.modules.keys() if k.startswith('http')]:
        del sys.modules[k]
    sys.meta_path.insert(0, Finder())

Do you really want to delete all already-loaded modules that start with 'http'? How about just a whitelist of names and prefixes (if necessary)? If someone tries to use their "httputils" module they might be surprised. There are 58 distributions on pypi that start with "http":

$ curl -s 'https://pypi.python.org/pypi?%3Aaction=index' | grep pypi/http | wc
58

$ curl -s 'https://pypi.python.org/pypi?%3Aaction=index' | grep pypi/http | head -5
 <td><a href="/pypi/http/0.02">http&nbsp;0.02</a></td>
 <td><a href="/pypi/http1/0.3.1">http1&nbsp;0.3.1</a></td>
 <td><a href="/pypi/http2/0.0.0-dev">http2&nbsp;0.0.0-dev</a></td>
 <td><a href="/pypi/httpagentparser/1.7.6">httpagentparser&nbsp;1.7.6</a></td>
 <td><a href="/pypi/httpappengine/0.1.9">httpappengine&nbsp;0.1.9</a></td>