Repository navigation
Abstract classes derived from built-in classes don't block instance creation #75310
Description
| BPO | 31127 |
|---|---|
| Nosy | @bitdancer |
| Superseder |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
Show more details
GitHub fields:
assignee = None
closed_at = <Date 2017-08-06.21:39:14.711>
created_at = <Date 2017-08-06.19:00:42.367>
labels = ['type-bug', 'library', 'docs']
title = "Abstract classes derived from built-in classes don't block instance creation"
updated_at = <Date 2017-08-06.21:39:14.709>
user = 'https://bugs.python.org/KevinShweh'bugs.python.org fields:
activity = <Date 2017-08-06.21:39:14.709>
actor = 'r.david.murray'
assignee = 'docs@python'
closed = True
closed_date = <Date 2017-08-06.21:39:14.711>
closer = 'r.david.murray'
components = ['Documentation', 'Library (Lib)']
creation = <Date 2017-08-06.19:00:42.367>
creator = 'Kevin Shweh'
dependencies = []
files = []
hgrepos = []
issue_num = 31127
keywords = []
message_count = 2.0
messages = ['299810', '299814']
nosy_count = 3.0
nosy_names = ['r.david.murray', 'docs@python', 'Kevin Shweh']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '5996'
type = 'behavior'
url = 'https://bugs.python.org/issue31127'
versions = ['Python 2.7', 'Python 3.6']
Activity
KevinShweh commentedon Aug 6, 2017
The only check that prevents instantiating abstract classes is in object.__new__, but most built-in classes never actually call object.__new__. That means you can do stuff like
and the Foo() call will silently succeed.
Ideally, the Foo() call should fail. Other options include having the Foo class definition itself fail, or just making a note in the documentation describing the limitation. (As far as I can see, this is currently undocumented.)
bitdancer commentedon Aug 6, 2017
This is a duplidate of bpo-5996. It is not clear if we are going to treat it as a bug or a doc bug.