I2C problem with scanning and filestore

[james-drummond]

PICO firmware: MicroPython v1.20.0 on 2023-04-26;
I2C device: one PCA9535 on the bus with 10k pull-up resistors
Using Thonny 4.1.1

The code is

from machine import Pin,I2C
i2c = I2C(0,scl=Pin(21),sda=Pin(20),freq=400000)
while True:
    i2c.scan()
print('Done')

If I put it into a file on my computer and then run it in Thonny - there is no scan result and no 'Done'
but
If I copy and paste the code directly into the Pico micropython interpreter then the scan results to [34] (the right number)

In both cases, I see traffic on the bus, and eyeballing it the traces look the same

I'm baffled. Any help appreciated

[robert-hh]

That looks something caused by "Thonny-Magic". In it's attempt to be "user-friendly", Thonny does a lot of things under the hood, affecting the expected behavior. It should work better when you use e.g. mpremote.

Anyway, you should code print(i2c.scan()) to see the scan result when the code is executed from a file.

[rkompass]

If you do the i2c.scan() in a while loop without wrapping a print() around it, it's return value, the array [34], is not displayed.
If you do it in the REPL then you see the returned value, because the REPL always tries to print the result of the last command entered.

[james-drummond]

Thanks people I appreciate the help - the main problem was in my brain.

Jim