Open d7cbc030-3f74-4bd2-b60c-3c530dccbaa8 opened 5 years ago
When declaring a dataclass with makedataclass, it is valid to omit type information for fields. \_annotations__ understands it and just adds typing.Any, but typing.get_type_hints fails with a cryptic error message:
>>> import dataclasses
>>> import typing
>>> A = dataclasses.make_dataclass('A', ['a_var'])
>>> A.__annotations__
{'a_var': 'typing.Any'}
>>> typing.get_type_hints(A)
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "/user/venvs/python_3.7/lib/python3.7/typing.py", line 973, in get_type_hints
value = _eval_type(value, base_globals, localns)
File "/user/venvs/python_3.7/lib/python3.7/typing.py", line 260, in _eval_type
return t._evaluate(globalns, localns)
File "/user/venvs/python_3.7/lib/python3.7/typing.py", line 464, in _evaluate
eval(self.__forward_code__, globalns, localns),
File "<string>", line 1, in <module>
NameError: name 'typing' is not defined
Adding typing.Any explicitly is an obvious workaround:
>>> B = dataclasses.make_dataclass('B', [('a_var', typing.Any)])
>>> typing.get_type_hints(B)
{'a_var': typing.Any}
There is already a bug filed regarding datalcasses and get_type_hints which might be related: https://bugs.python.org/issue34776
It looks like https://github.com/python/cpython/pull/9518 will fix also this one.
I'm not sure what can be done with this. The problem is that the decorator doesn't know what's in the caller's namespace. The type being added is "typing.Any". If the caller doesn't import typing, then get_type_hints will fail (as demonstrated here).
The only thing I can think of is using a type that's in builtins. "object" springs to mine, but of course that's semantically incorrect.
Or, maybe I could use "dataclasses.sys.modules['typing'].Any". I don't currently import sys (I don't think), but this should be a cheap import. Then if typing.get_type_hints() is called, we know typing will have already been importing.
But what if "dataclasses" isn't in the caller's namespace? I guess if I could find some way to navigate to sys.modules from __builtins__, that would largely work, absent playing games with builtins.
I'm not sure what can be done with this. The problem is that the decorator doesn't know what's in the caller's namespace. The type being added is "typing.Any". If the caller doesn't import typing, then get_type_hints will fail (as demonstrated here).
IIUC the main problem is that get_type_hints() fails even if typing is imported. I would expect this to work (just repeating the original example in a more compact form):
import dataclasses
import typing
A = dataclasses.make_dataclass('A', ['a_var'])
typing.get_type_hints(A) # This currently crashes
Interestingly, if I use a very similar call that it works:
>>> typing.get_type_hints(A, globalns=globals())
{'a_var': typing.Any}
So the core of the issue is that the globals are identified incorrectly, and indeed if I look at the generated class it looks wrong:
>>> A.__module__
'types' # Should be '__main__'
I think we should fix the __module__
attribute of the dynamically generated dataclasses (for example the way it is done for named tuples).
Btw, https://github.com/python/cpython/pull/14166 may potentially fix the __module__
attribute here too.
PR 14166 does not fix this issue.
Reproduced on 3.11.07a
I ran into this when trying to make a quick dataclass to demo cattrs
code generation.
import dataclasses
import cattrs
A = dataclasses.make_dataclass('A', ['a_var'])
a = A("a_value")
cattrs.unstructure(a)
NameError: name 'typing' is not defined. Did you forget to import 'typing'?
Initially I thought this was a cattrs bug, but on looking at the trace it uses get_type_hints
so it's related to this same issue.
In 3.13.0b4, 3.12, 3.11 (and earlier) this still reproduces with:
import dataclasses
from typing import get_type_hints
A = dataclasses.make_dataclass('A', ['a_var'])
print(get_type_hints(A))
However, in 3.13.0b4, and 3.12 (but not 3.11 or earlier) if you plainly import typing
this now "works" - I think because __module__
is now set when it was not in 3.11:
import dataclasses
import typing
A = dataclasses.make_dataclass('A', ['a_var'])
print(typing.get_type_hints(A))
I say "works" because it's evaluating the name 'typing' from the script file that defines the dataclass. Unlikely someone would do this, but I'd still consider this incorrect behaviour.
import dataclasses
from typing import get_type_hints
class typing:
Any = int
A = dataclasses.make_dataclass('A', ['a_var'])
print(get_type_hints(A))
{'a_var': <class 'int'>}
It also fails if A is defined in a file that doesn't import typing
and typing.get_type_hints
is used from a separate file. Likewise if inspect.get_annotations(..., eval_str=True)
is used you get the same error without typing
needing to be imported anywhere.
Some possible solutions:
typing.Any
object.__annotations__
after the dataclass has been created
__annotations__
__annotations__
that will import and return typing.Any
for untyped fields on demand.
Put a dict-like object in annotations that will import and return typing.Any for untyped fields on demand.
I think that this is a proper solution. This will be fixed after __annotate__
will be fully supported.
If you want to avoid importing typing
for the creation of such a class you still have to temporarily put something else in place for dataclasses to use in construction, and then replace it with something that will correctly evaluate afterwards. Otherwise dataclasses will trigger the imports when it inspects the annotations to create the class in the first place.
PEP649/749 could change things, but can/should this also be fixed for 3.13/3.12?
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: ```python assignee = 'https://github.com/ericvsmith' closed_at = None created_at =
labels = ['3.8', 'type-bug', '3.7']
title = 'get_type_hints fails if there are un-annotated fields in a dataclass'
updated_at =
user = 'https://github.com/a-recknagel'
```
bugs.python.org fields:
```python
activity =
actor = 'serhiy.storchaka'
assignee = 'eric.smith'
closed = False
closed_date = None
closer = None
components = []
creation =
creator = 'arne'
dependencies = []
files = []
hgrepos = []
issue_num = 37948
keywords = []
message_count = 5.0
messages = ['350488', '350973', '355559', '356829', '363662']
nosy_count = 4.0
nosy_names = ['eric.smith', 'serhiy.storchaka', 'levkivskyi', 'arne']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37948'
versions = ['Python 3.7', 'Python 3.8']
```
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