Django automatically adding ".xlsx" to mimetypes types_map

Using Django Mystery Errors
1

Hi all,

Python’s built-in mimetypes library has a method types_map(), which returns a mapping of filename extensions → MIME type. The mapping looks like {'.js': 'application/javascript', '.mpeg': 'video/mpeg', ...}.

I’ve noticed that when using a vanilla Python shell there is no mapping for .xlsx, but when using Django’s shell (python manage.py shell) there is.

Repo steps:

In vanilla Python shell:

import mimetypes
print(mimetypes.types_map[".xlsx"]) # Errors

In Django shell:

import mimetypes
print(mimetypes.types_map[".xlsx"]) # Prints "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"

Django Version: 4.2
Python Version: 3.11.10 (I also tried 3.8)

Mimetypes does provide the add_types() method which adds a new extension to the mapping. However, I could not find anything in the Django source code using it or otherwise affecting the mapping.

Any ideas about where this .xlsx mapping is coming from?

2

When you use the Django shell, does your environment include any other extra modules besides Django?

3

Good call, that was it. It looks like the openpyxl package adds some file extensions to the mapping when initialized. Thanks for the help.