One annoyance when implementing __getitem__() is debugging the slice syntax interactively .. Below you can see an example.
First you create a dummy class with simple method that print its arguments.
Then you can experiment.
class Blah:
def __getitem__(self,*args):
print(args)
return args
b = Blah()
b[1]
b[2:5]
b[::2,2:11:2]
s = b[::3]
print()
#filling the indices
ind = s[0].indices(12)
print(f'indices: {s[0]} => {ind}')
#make it a range
rng = range(*s[0].indices(12))
print(f'range: {rng}')
for i in rng: print(i)
(1,) (slice(2, 5, None),) ((slice(None, None, 2), slice(2, 11, 2)),) (slice(None, None, 3),) indecies: slice(None, None, 3) => (0, 12, 3) range: range(0, 12, 3) 0 3 6 9
In addition inside your method you can convert a slice to a range by using the .indices() method … and then use them to do processing in a loop.
