Dynamic default value #1210
Dynamic default value #1210
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Discussed in #866 So I would like to see this: from datetime import datetime
from pydantic import BaseModel
class Record(BaseModel):
name: str
description: str
ts: datetime = datetime.now
record = Record(name='Foo', description='Bar and Baz also.')
print(record.ts)
#> 2020-02-06 22:11:43.454720However if type of field is callable, it must remain untouched: from random import randint
from typing import Callable
from pydantic import BaseModel
class IntGenerator(BaseModel):
fabric: Callable[..., int] = randint
generator = IntGenerator()
print(generator.fabric(0, 1))
#> 1@samuelcolvin, any thoughts? |
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@MrMrRobat Thanks ! I thought about the implementation with |
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Mostly looks goods, needs tests fixing and docs.
pydantic/fields.py
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| def __init__(self, default: Any, **kwargs: Any) -> None: | ||
| def __init__(self, default: Any = Undefined, *, default_factory: Any = None, **kwargs: Any) -> None: | ||
| if default is not Undefined and default_factory is not None: |
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perhaps better to move this check into Fieldm then you can use pop() as is done elsewhere.
pydantic/fields.py
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| default: Any, | ||
| default: Any = Undefined, | ||
| *, | ||
| default_factory: Any = None, |
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| default_factory: Any = None, | |
| default_factory: Optional[Callable[[], Any]] = None, |
or something
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I'm keen on the approach of from datetime import datetime
from pydantic import BaseModel
class Record(BaseModel):
ts: datetime = datetime.nowHowever I think it could cause subtle changes in behaviour in edge cases so let's wait for v2. Getting |
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| # With a callable: we still should be able to set callables as defaults | ||
| class FunctionModel(BaseModel): | ||
| a: int = 1 | ||
| uid: Callable[[], UUID] = Field(uuid4) |
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Had to use = Field(uuid) instead of = uuid4 as functions are ignored when creating fields and the default is hence not properly set
I think this behaviour should be fixed but in another PR (maybe for v2 with the other syntax for dynamic values)
pydantic/fields.py
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| default: Any, | ||
| default: Any = Undefined, | ||
| *, | ||
| default_factory: Optional['Callable[[], Any]'] = None, |
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Had to use 'Callable...' because it would raise
TypeError: 'ABCMeta' object is not subscriptable
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How is that possible? It already used in this module without an issues. That could be the case for collections.Callable, but it's a different thing.
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Ah right ! I didnt' see the Callable came from .typing. Thanks !
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There's a chance we might need to change the signature or behaviour of default_factory in future.
Therefore might be useful to comment in the documentation that this feature is provisional and might change in future minor releases? See #1179 for an example.
Otherwise looking good.
changes/1210-prettywood.md
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| Add `default_factory` `Field` argument to create a dynamic default value by passing a zero-argument callable. | |||
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| Add `default_factory` `Field` argument to create a dynamic default value by passing a zero-argument callable. | |
| Add `default_factory` argument to `Field` to create a dynamic default value by passing a zero-argument callable. |
pydantic/fields.py
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| from typing import ( | ||
| TYPE_CHECKING, | ||
| Any, | ||
| Callable, |
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if the below is TypingCallable, what is this? Maybe good to give this an alias.
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I decided to add a NoArgAnyCallable directly in the local typing module. Makes things clearer imo
pydantic/fields.py
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| """ | ||
| if self.default is not None and self.type_ is None: | ||
| self.type_ = type(self.default) | ||
| default_value = self.default_factory() if self.default_factory is not None else self.default |
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perhaps useful to have a get_default() function on this class which is used here and in main.py and perhaps deals with deepcopy?
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@samuelcolvin Thanks for the review ! Changes done |
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otherwise looks good, sorry I missed this before.
Co-Authored-By: Samuel Colvin <samcolvin@gmail.com>
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@samuelcolvin When do you think a release will be ready with this PR? Looking forward to it! |
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@jmagnusson see #1341 for details on release date. |
Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Change Summary
Following #155 and #866, here is a proposal of implementation to simplify dynamic default values
Right now, to have a dynamic default value, we need to use
validatorslikeNow, we can use
default_factory(same name as dataclasses.to be consistent)Related issue number
#155 and #866
Checklist
changes/<pull request or issue id>-<github username>.mdfile added describing change(see changes/README.md for details)