How can I make Python "import.util.module_from_spec" work more like "import""?

Is the module ever executed? If not, the assignment or declaration within the module has not yet put the child objects into the __dir__ of the module object. From the version of this function in the standard file loader, when you call module_from_spec all you get is the module, and the members that logically belong to all modules. It has no contents.

(The system may load modules on different paths or in different states of use with other Loader objects, which may complicate this task overall. For sys.path, for instance, the module you get seems to be populated already. Bear in mind that there is a sub-object here for a reason. There is not just one Python Loader.)

If it is not already loaded, to get the module object populated, you would call

module_spec.loader.exec_module(module)

(If it exists.)

For example on Python 3.8:

import importlib
module_spec = importlib.util.find_spec('textwrap')
module = importlib.util.module_from_spec(module_spec)
module_spec.loader.exec_module(module)
print(module.fill)

will output:

<function fill at 0x7fae70e6fd90>

In older versions of Python, exec_module is missing, and you need to call:

module_spec.loader.load_module(module.__name__)

On 3.6 and later, however, the code above works as expected.

The information was gleaned by looking at importlib._bootstrap.py::_exec, and the things that it calls.

There is still a question here as to whether imports inside the loaded module will end up in the global namespace, or your own. But that is another issue.

The issue is with importlib. For some reason, it didn't load all module attributes.

Let's go through the below cases:

Case 01 - Code:

import importlib


module_spec = importlib.util.find_spec("textwrap")
textwrap_module = importlib.util.module_from_spec(module_spec)
submodule = "fill"
print(f'Attributes: {dir(textwrap_module)}')
print(f'Attribute Found: {hasattr(textwrap_module, submodule)}')

Case 01 - Output:

Attributes: ['__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__']
Attribute Found: False

As you can see, in the attributes list, there's no attribute named fill. That's why it returns False.

Case 02 - Code:

import textwrap


print(f'Attributes: {dir(textwrap)}')
print(f'Attribute Found: {hasattr(textwrap, submodule)}') # True

Case 02 - Output:

Attributes: ['TextWrapper', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', '_leading_whitespace_re', '_whitespace', '_whitespace_only_re', 'dedent', 'fill', 'indent', 're', 'shorten', 'wrap']
Attribute Found: True

In this case, you can see in the attributes list, there's an attribute named fill. That's why it returns True.

Reason Behind This

# Bootstrap help #####################################################

# Until bootstrapping is complete, DO NOT import any modules that attempt
# to import importlib._bootstrap (directly or indirectly). Since this
# partially initialised package would be present in sys.modules, those
# modules would get an uninitialised copy of the source version, instead
# of a fully initialised version (either the frozen one or the one
# initialised below if the frozen one is not available).

• Reference for Python 3.9: importlib/__init__.py
• Reference for Python 3.8: importlib/__init__.py
• Reference for Python 3.4: importlib/__init__.py

Conclusion:

By analyzing the above two cases, we can say that importing modules through importlib works differently from the builtin import statement because of the above mentioned reason.