Injecting variables into an import namespace

Question

To illustrate what I am trying to do, let\'s say I have a module testmod that lives in ./testmod.py. The entire contents of this module is

Answer 1

You could screw with Python's builtins to inject your own fake built-in test variable:

import builtins    # __builtin__, no s, in Python 2

builtins.test = 5  # or whatever other placeholder value

import testmod

del builtins.test  # clean up after ourselves

Answer 2

I came up with a solution based on this answer and the importlib docs. Basically, I have access to the module object before it is loaded by using the correct sequence of calls to importlib:

from importlib.util import spec_from_file_location, module_from_spec
from os.path import splitext, basename

def loadConfig(fileName):
    test = 'This is a test'
    name = splitext(basename(fileName))[0]
    spec = spec_from_file_location(name, fileName)
    config = module_from_spec(spec)
    config.test = test
    spec.loader.exec_module(config)
    return config

testmod = loadConfig('./testmod.py')

This is a bit better than modifying builtins, which may have unintended consequences in other parts of the program, and may also restrict the names I can pass in to the module.

I decided to put all the configuration items into a single field accessible at load time, which I named config. This allows me to do the following in testmod:

if 'test' in config:
    x = config['test']

The loader now looks like this:

from importlib.util import spec_from_file_location, module_from_spec
from os.path import splitext, basename

def loadConfig(fileName, **kwargs):
    name = splitext(basename(fileName))[0]
    spec = spec_from_file_location(name, fileName)
    config = module_from_spec(spec)
    config.config = kwargs
    spec.loader.exec_module(config)
    return config

testmod = loadConfig('./testmod.py', test='This is a test')