Kivy stopped without returning error message

Hi I have a pretty complex kivy application. I was doing some stuff, I started the app but when I was trying to save the data, my app suddenly stopped without any error message: Process finished with exit code 1

After reflexion, I found out that I deleted a key on the dict I was iterating on !

So I should have seen RuntimeError: dictionary changed size during iteration but nothing appeared ! Why and how to prevent this ?

(it can take al ong time to debug, I can't imagine without error message !).

Here is an example of a code that raise the needed error:

d = {"a":"e","b":"c"}for k in d:    del d[k]