Slicing Context raises KeyError in Python 3.6

[BigRoy]

Issue

In our plug-ins we've been doing context[:] to get a copy of the instances list from the context, though in Python 3.6 this is giving us the following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "D:\pyblish-base\pyblish\plugin.py", line 771, in __getitem__
    raise KeyError("%s not in list" % item)
KeyError: 'slice(None, None, None) not in list'

Confirmed and reproducable with:

import pyblish.api as api

c = api.Context()
print(c[:])

This works in Python 2.7 - but raises the error above in Python 3.6.

Workaround

It does however work when doing list(context) to get a copy of the list.

import pyblish.api as api

c = api.Context()
print(list(c))

---

Shouldn't the first one also work if it "should behave" like a regular list?

[BigRoy]

It seems to be coming from this line.

Refactoring it to:

        if isinstance(item, (int, slice)):

Allows the slicing to function as in a regular Python list in both Python 2.7 and Python 3.6.

---

Why it's working without this in Python 2.7 on the other hand makes me confused now.
It seems in Python 2.7 that with slicing it never enters the __getitem__ function. :)

More info:

• Python Slice object
• StackOverflow: Python Implementing Slicing in __getitem__