Mailman 3 unsubscriptable vs object does not support indexing - Python-Dev

23 Sep 2009

      Is there a reason or a rule by which CPython reports different error message for different failures to subscript?

For example:
...
...
...
set()[2]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'set' object does not support indexing
class c(object): pass
...
c()[2]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'c' object does not support indexing
But compare this to:
...
...
...
[].append[42]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'builtin_function_or_method' object is unsubscriptable
(lambda: 42)[42]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'function' object is unsubscriptable
property()[42]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'property' object is unsubscriptable
IronPython had a bug report that we were getting this wrong for set objects and that "does not support indexing" was also a clearer error message.  I'm wondering if there's some reason why the different error messages occur which I'm missing.   Otherwise I could switch to using the more clear message or start marking types which should report the unsubscriptable error.  Does anyone have any insights into this?

unsubscriptable vs object does not support indexing

Dino Viehland

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