Add multiple extensions in one filetypes mac - tkinter/filedialog/askopenfilename

It seems that you must separate the wildcard patterns with a space rather than ; (verified on Python 3.5.1):

from tkinter import filedialog

# add `, initialdir="..."` to set the initial directory shown in the dialog
filedialog.askopenfilename(filetypes=[("Excel files", ".xlsx .xls")])

Note:

• While "*.xlsx *.xls" would work too (at least on Windows and macOS), the initial * isn't necessary.^[1]
• Whether .* or *.* works (no filter) seems to be platform-dependent; omitting filetypes is the better option in that case.
• Similarly, the behavior of matching part of the base filename - something like foo.txt or foo*.txt - appears to be platform-dependent: on Windows, these do work, with a prepended * (*foo.txt and *foo*.txt), whereas on macOS they seem to match nothing.

^{If the platform-dependent behaviors are instead / also lined to different tkinter versions, do let us know.}

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^{[1] Jakub Bláha reports that "*.xlsx *.xls" didn't actually work for him in Python 3.7.4 on Windows 10 version 1903 (though I don't see the same problem); to be safe, omit the * if not needed.}

At least on Windows, if you want to be able to open multiple filetypes but always only one at a time, your code has to look like this:

filedialog.askopenfilename(filetypes=[("Excel file","*.xlsx"),("Excel file 97-2003","*.xls")])

If you want to be able to select both file types at the same time without switching between them, they need to have the same name.

filedialog.askopenfilename(filetypes=[("Excel file","*.xlsx"),("Excel file", "*.xls")])