[Question] FilePicker, manage filter for files without extension

[MrDIDJoy]

Question

I need the user to be able to select only files WITHOUT an extension when activating FilePicker. How do I specify this in allowed_extensions? And is there any way to do this?

Code sample

No response

Error message

No response

------------------------------------------------------

• I have searched for answers to my question both in the issues and in previous discussions.

[kokoc30]

allowed_extensions is a positive list of extensions, such as ["txt", "csv"], used with FilePickerFileType.CUSTOM. There isn't a documented, portable “extensionless files only” filter. An empty string in that list is not a reliable cross-platform solution for the native dialogs.

Use FilePickerFileType.ANY, then validate the selected names before accepting or processing them:

from pathlib import PurePath


def require_extensionless(files):
    files = files or []
    rejected = [f.name for f in files if PurePath(f.name).suffix]
    if rejected:
        raise ValueError(
            "Choose files without an extension: " + ", ".join(rejected)
        )
    return files

In the older event-based FilePicker API, apply this to e.files in on_result. In the current async API, apply it to the returned list:

files = await picker.pick_files(file_type=ft.FilePickerFileType.ANY)
try:
    accepted = require_extensionless(files)
except ValueError as error:
    # Show str(error) in your UI; do not process the rejected selection.
    return
# Process accepted here; [] also covers cancellation.

This validates after selection; files with extensions remain visible in the native picker. If hiding them is essential, you would need a custom file-browser UI rather than an extension allowlist.

PurePath(...).suffix checks the filename without opening the file. Under that definition, a dotfile such as .env has no suffix. If your rule is instead “no dot anywhere in the filename,” use '.' in f.name for the rejection condition.

References: Flet FilePicker options, Python suffix semantics.