How to open a file in a package with importlib?

I am trying to put the back-end of a simple web-scraping application that I'm working on into a package, but this application relies on loading from a pickled python object, which I'm unable to load into the file with importlib. Before, when I had all the code in a single file, and relied on open(), all worked fine, but now I get an error when I import the package. After this error, I tried loading the file with importlib, and could not make it work.

I am following the steps in this answer from a similar question: How to read a (static) file from inside a Python package?.

The file structure in my package is:

mypackage\
        __init__.py
        parse.py
        search.py
        categories\
                categories.pickle
                generate_categories_if_corrupted.py

The content of init.py:

from %mymodule% import search

The code where the error happens:

import importlib.resources as resources
from pickle import load
from . import categories

try:
    with resources.open_binary(categories, "categories.pickle") as cat:
        CATS = load(cat)
except FileNotFoundError:
    raise FileNotFoundError("")

The error:

Traceback (most recent call last):
  File "%mypackage%\parse.py", line 15, in <module>
    with resources.open_binary(categories, "categories.pickle") as cat:
  File "C:\Users\%me%\AppData\Local\Programs\Python\Python38\lib\importlib\resources.py", line 92, in open_binary
    _check_location(package)
  File "C:\Users\%me%\AppData\Local\Programs\Python\Python38\lib\importlib\resources.py", line 82, in _check_location
    raise FileNotFoundError(f'Package has no location {package!r}')
FileNotFoundError: Package has no location <module '%mypackage%.categories' (namespace)>

During handling of the above exception, another exception occurred:

## just a  FileNotFoundError with an error message, as expected.

How do I fix this? It's my first time trying to make my code into a package in Python.

Thanks in advance for your answers.