Unexpected errors in __iter__ are masked in "in" and the operator module

[serhiy-storchaka]

BPO	40824
Nosy	@ned-deily, @serhiy-storchaka, @miss-islington
PRs	bpo-40824: Do not mask errors in __iter__ in "in" and the operator module. #20537 [3.9] bpo-40824: Do not mask errors in __iter__ in "in" and the operator module. (GH-20537) #21043 [3.8] bpo-40824: Do not mask errors in __iter__ in "in" and the operator module. (GH-20537) #21044 [3.7] bpo-40824: Do not mask errors in __iter__ in "in" and the operator module. (GH-20537) #21045 [3.6] bpo-40824: Do not mask errors in __iter__ in "in" and the operator module. (GH-20537) #21046

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-06-22.09:35:14.853>
created_at = <Date 2020-05-30.11:36:12.337>
labels = ['interpreter-core', 'type-bug', '3.8', '3.9', '3.10']
title = 'Unexpected errors in __iter__ are masked in "in" and the operator module'
updated_at = <Date 2020-06-24.09:11:43.783>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2020-06-24.09:11:43.783>
actor = 'ned.deily'
assignee = 'none'
closed = True
closed_date = <Date 2020-06-22.09:35:14.853>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2020-05-30.11:36:12.337>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 40824
keywords = ['patch']
message_count = 6.0
messages = ['370372', '372039', '372044', '372045', '372238', '372240']
nosy_count = 3.0
nosy_names = ['ned.deily', 'serhiy.storchaka', 'miss-islington']
pr_nums = ['20537', '21043', '21044', '21045', '21046']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40824'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[serhiy-storchaka]

All errors raised in the __iter__ method are masked by the TypeError exception in the "in" operator and functions operator.contains(), operator.indexOf() and operator.countOf().

>>> class BadIterable:
...     def __iter__(self):
...         1/0
... 
>>> 
>>> 1 in BadIterable()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: argument of type 'BadIterable' is not iterable

It includes exceptions out of control of the programmer like MemoryError and KeyboardInterrupt. Converting them to TypeError can lead to weird errors or incorrect results.

See also similar bpo-26407.

[serhiy-storchaka]

New changeset cafe1b6 by Serhiy Storchaka in branch 'master':
bpo-40824: Do not mask errors in __iter__ in "in" and the operator module. (GH-20537)
cafe1b6

[miss-islington]

New changeset 353c4ba by Miss Islington (bot) in branch '3.9':
bpo-40824: Do not mask errors in __iter__ in "in" and the operator module. (GH-20537)
353c4ba

[miss-islington]

New changeset b99824a by Miss Islington (bot) in branch '3.8':
bpo-40824: Do not mask errors in __iter__ in "in" and the operator module. (GH-20537)
b99824a

[ned-deily]

@serhiy, you have opened PRs for this for 3.7 and 3.6, both of which are now in the security-fix phase of their release cycles. It looks like this behavior has been around for a long time and does not appear to be a security issue. Unless there is some important reason why this behavior should be changed in a security fix release (for 3.6) or as a release critical fix for 3.7.8 final and unless another core developer reviews the changes, I do not think the PRs should be merged to 3.7 or 3.6.

[serhiy-storchaka]

Sorry, I was not sure which versions are in security-fix phase now.