readdir case-insensitive wildcard

[1Map]

I work in Windows.

How would I go about looking for files like, for example, both:
*.txt and *.TXT

glob.readdir returns either the one or the other, but not both.

For example I have 2 files:
file1.txt
file2.TXT

Now, I want to find all files with extension txt (Upper and Lower case). How would I do that without calling 2 functions (*.txt and *.TXT) ?