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TypedDict missing many dict methods #3843
Description
mypy isn't recognizing methods of TypedDict.
- mypy 0.521
- mypy_extensions 0.3.0
- typeshed 0.0.1
from mypy_extensions import TypedDict
D = TypedDict('D', {'a': int})
d = {'a': 4} # type: D
d.copy()
d.get('a')
d.clear()
d.setdefault('b', 7)
d.has_key('a')
d.items()
d.keys()
d.values()
d.iteritems()
d.iterkeys()
d.itervalues()
d.pop('b', None)
d.popitem()
d.update({'f': 11})
d.viewitems()
d.viewkeys()
d.viewvalues()
"""
$ mypy -2 example.py
example.py:7: error: "D" has no attribute "copy"
example.py:9: error: "D" has no attribute "clear"
example.py:10: error: "D" has no attribute "setdefault"
example.py:11: error: "D" has no attribute "has_key"
example.py:18: error: "D" has no attribute "pop"
example.py:19: error: "D" has no attribute "popitem"
example.py:20: error: "D" has no attribute "update"
example.py:21: error: "D" has no attribute "viewitems"
example.py:22: error: "D" has no attribute "viewkeys"
example.py:23: error: "D" has no attribute "viewvalues"
"""
Activity
teepark commentedon Aug 18, 2017
@douglas-treadwell
JelleZijlstra commentedon Aug 18, 2017
This is already tracked in #3518, but you're listing more methods. A lot of these shouldn't be hard to do, so feel free to submit a PR.
I wonder if there's also a way to inherit them from the
dictstubs somehow.teepark commentedon Aug 18, 2017
I did find that ticket, but since he marked it as a feature and not a bug I figured the "special casing" refers to adding special behaviors to the listed methods (like
clearis probably currently expected to return aDict[Any, Any]but could return an instance of the current type).teepark commentedon Aug 18, 2017
It seems suspiciously like a mypy bug because typeshed should be forcing it to produce a
Type[dict]. I'm not sure what else the stubs could be doing to help.ilevkivskyi commentedon Aug 18, 2017
I think the root of the problem is that the fallback for TypedDicts is
Mappingand notDict, and the former has much fewer methods. A hacky way to fix this would be to define a special subclass ofMappingthat will defineDictmethods that are safe to use for TypedDicts, and use it instead for fallbacks.JelleZijlstra commentedon Aug 18, 2017
Why isn't the fallback for TypedDict just Dict?
ilevkivskyi commentedon Aug 18, 2017
IIRC this is because some methods of
Dictare not safe since they can change dictionary items "en masse", while__getitem__/__setitem__are special-cased to allow only certain keys/types. Now I am not sure it was the best decision (although more safe/conservative).JukkaL commentedon Feb 1, 2018
A user just asked about how to
.copy()a TypedDict, and apparently the most reasonable approach is to use a cast, which is unfortunate.Note that some of the methods aren't always safe, such as
clear()for a total typed dict.JukkaL commentedon Nov 16, 2018
Here's a quick analysis of each missing method:
copy: Simpleclear: Not safe, due to structural subtyping (may delete a required key)setdefault: Need to provide type context for the second argument; require literal keyhas_key: Python 2 only, simplepop: Require literal key; only valid for non-required keyspopitem: Not safe, due to structural subtyping (may delete a required key)update: Should provide TypedDict type context for the positional argument; needs special casing for keyword argumentsviewitems: Python 2 only, similar to Python 3items()viewkeys: Python 2 only, similar to Python 3keys()viewvalues: Python 2 only, similar to Python 3values()Add support for additional TypedDict methods (#6011)
nguyenbathanh commentedon Dec 31, 2018
@JukkaL When can we release it? I didn't found it in latest version
v0.650.Thanks.
emmatyping commentedon Dec 31, 2018
@nguyenbathanh releases are usually done every few weeks, but due to holidays I expect it will take a bit longer between
0.650and0.660. For now you can use the development branch if you really need this fix. (e.g.pip3 install git+https://github.com/python/mypy.git).nguyenbathanh commentedon Jan 1, 2019
@ethanhs Thanks for your information! I will use the Dev version.