The order of execution

[krismc]

I sometimes have a guess at the sequence in which upython does things and come up wrong. In the examples below boot_modem & _attached() are functions that return 'OK' or None.

If I run

r=0
r=boot_modem() and _attached()
if r and 'OK' in r:

all is good. But my original idea

r=0
if r:=(boot_modem() and attached()) and 'OK' in r:

crashes saying integers aren't iterable, which means the walrus hasn't run before the 'OK' in r check & r must still be zero. I don't understand why that is?

[GitHubsSilverBullet]

The ›new‹ r hasn't been defined at this point, the ›old‹ r is still an integer 0.
Thus you're testing whether 'OK' is in 0.
Try:

    if (r := (boot_modem() and attached())) and 'OK' in r:

and all is well.

[peterhinch]

Yes. It's usually wise to put assignment expressions in parens. The following works as expected:

>>> r = 0
>>> if (r:= 1) and r==1: print(f"r = {r}")
... 
r = 1

But this does not:

>>> r = 0
>>> if r:= 1 and r==1: print(f"r = {r}")
... 
>>> r
False
>>> 

because the latter is effectively doing

if r:= (1 and r==1): print(f"r = {r}

which sets r False (because the comparison returns False).

[krismc]

That makes sense Peter, tnx. Now that I understand no need to add it to my list of python mongrel.