Someone changed the file permissions

It turns out the whole thing was caused when someone from Technical Support decided to change the permissions on the deliveries . txt file, making it read-only. When the system tried to write deliveries into the file, it failed. But what's worse, it failed silendy:

Because no error message appeared in the GUI, the trainee thinks everything is OK.

"deliveries.txt" was made readonly.

deliveries.txt

The error in the Python Shell was not noticed by the trainee.

"deliveries.txt" was made readonly.

The error in the Python Shell was not noticed by the trainee.

When you were writing programs that ran in the Python Shell, you could always tell when it failed: a huge, ugly error message appeared. Why not with GUIs? Don't they do the same?

They do, but the trouble is that the message appears in the Shell and your user is busy looking at the nice GUI, so the ugly error can often be missed.

When using a GUI, how do you spot errors? Once spotted, what happens then?

Note: To reproduce this error on your PC, you need to make your deliveries . txt file read-only. How you do this depends upon your operating system. If you are unsure how to make a file read-only, check the Web for more advice (or ask a friendly local guru). On most systems, it involves editing the properties of the file.

making an exception

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