flet build macos now supports NumPy (official bug-fix)

There was a bug in Flet (version 0.21.0 and 0.21.1) that caused built app with NumPy for macOS to crash immediately after launch. I reported this issue on GitHub some time ago, and finally Feodor Fitsner, the author, updated me with a solution. To fix the issue, you simply need to build your Flet app again.


Template for Flet version 0.21.2 and the latest version 0.22.0 (as of April 19, 2024) has been modified, according to the author. Flet itself has not been changed. Therefore, if you are using NumPy with a Flet app on macOS, you should be good to go with these versions. Just rebuild now (flet build macos) and it should work.

If you’re running older version of Flet, upgrade to the latest with pip install --upgrade flet. You can specify a version as well if needed:

pip install flet==0.21.2

I upgraded to 0.22.0 and confirmed my SPS Player app built for macOS with NumPy code didn’t crash by building it again. If not sure your Flet version, try the below command:

pip list|grep flet

# result will be like the below:
flet                  0.21.2
flet-core             0.21.2
flet-runtime          0.21.2

Another way

Adding the below code to your Flet will also resolves the issue, according to the comment in the issue. I won’t bother as long as my codes work with the recent Flet versions though.

import os

os.environ["OPENBLAS_NUM_THREADS"] = "1"

In the related issue you can find more, detailed info.

Thanks to the solution

Flet is open-source software that is available for free, so I didn’t request for update or pressure the author to fix anything. However, I am grateful that they took the time to address this issue and make Flet even better. To contribute to Flet, I continue developing my app with it.

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