import sys

class SempaiLoader(object):
    def __init__(self, *args):
        print args

    def find_module(self, fullname, path=None):
        print 'finding', fullname, path
        if fullname == 'simple':
            return self
        return None

sys.path_hooks.append(SempaiLoader)
sys.path.insert(0, 'simple')

import os
import sys

class SempaiLoader(object):

    def find_module(self, name, path=None):
        for d in sys.path:
            json_path = os.path.join(d, '{}.json'.format(name))
            if os.path.isfile(json_path):
                print json_path
                return self
        return None

    def load_module(self, name):
        raise ImportError('Hey, yo fool')

sys.meta_path.append(SempaiLoader())

Add the import hook to sys.meta_path
Add the import hook to sys.meta_path
