I cannot explain why there is a different behaviour with the same situation.
If I write:
im = (10, 20, [3, 4])
im[2] += [5, 6, 7, 8]
Then as expected I have this: "TypeError: 'tuple' object does not support item assignment".
If I handle the exception:
im = (10, 20, [3, 4])
print("im: {} - id(im): {}".format(im, id(im)))
print("im[2]: {} - id(im[2]: {})".format(im[2],id(im[2])))
try:
im[2] += [5, 6, 7, 8]
except:
pass
print("im: {} - id(im): {}".format(im, id(im)))
print("im[2]: {} - id(im[2]: {})".format(im[2],id(im[2])))
The console prints:
im: (10, 20, [3, 4]) - id(im): 1960340013184
im[2]: [3, 4] - id(im[2]: 1960339967232)
im: (10, 20, [3, 4, 5, 6, 7, 8]) - id(im): 1960340013184
im[2]: [3, 4, 5, 6, 7, 8] - id(im[2]: 1960339967232)
So the exception is raised and the list inside the tuple has been modified (even if the tuple is an immutable object). Until here no problem with this.
But, if I do this:
l=[3,4]
im = (10, 20, l)
l+= [5, 6, 7, 8]
then there is no exception raised, and by checking the id:
l=[3,4]
im = (10, 20, l)
print("im: {} - id(im): {}".format(im, id(im)))
print("l: {} - id(l): {}".format(l,id(l)))
l+= [5, 6, 7, 8]
print("im: {} - id(im): {}".format(im, id(im)))
print("l: {} - id(l): {}".format(l,id(l)))
I get in the console:
im: (10, 20, [3, 4]) - id(im): 2050054668416
l: [3, 4] - id(l): 2050054622528
im: (10, 20, [3, 4, 5, 6, 7, 8]) - id(im): 2050054668416
l: [3, 4, 5, 6, 7, 8] - id(l): 2050054622528
I don't understand why there is a different behaviour. I was expecting that the exception was raised in both case.
(I'am using Python 3.8.5)
