"from" keyword in data to validate raises an Syntax error

[vincestus]

Hello,

I'm running into a problem when validating the following data with pydantic:

{ "validity_dates": { "from": "2014-12-31", "to": "2015-12-31" } }
It's the "from" key in the data that is problematic:

class ValidityDates(pydantic.BaseModel): from: str to: str

This code raises a SyntaxError: invalid syntax. How can I map a supported class attribute like "from_" to the dict key "from" when:

1. validating the data
2. serialising the model

Thanks fo your help

[samuelcolvin]

from datetime import date
from pydantic import BaseModel


class Foobar(BaseModel):
    from_: date

    class Config:
        fields = {
            'from_': 'from'
        }


foobar = Foobar(**{'from': '2014-12-31'})
print(foobar)
print(repr(foobar.from_))

[samuelcolvin]

closing this, but feel free to comment if that doesn't solve your problem.

[vincestus]

Thanks for the fast answer. To have "form" as a keyword when serialising, I overwrote the "dict()" method as follows. Is there another way?

class ValidityDates(pydantic.BaseModel):
    
    class Config:
        fields = {
            'from_': 'from'
        }

    def dict(self, *, include=None, exclude=set()):
        d = dict()
        for k, v in self:
            if k not in exclude and (not include or k in include):
                if k == "from_":
                    d["from"] = v
                else:
                    d[k] = v
        return d

    from_: str
    to: str

[samuelcolvin]

No problem, surely

def dict(self, *args, **kwargs):
    d = super().dict(*args, **kwargs)
    d['from'] = d.pop('from_')
    return d

Would be simpler.

[vincestus]

Way better, thanks!

[likern]

I'd like to add this in documentation in section "How to handle JSON which contains fields reserved as keywords in Python" or similar. Because this special case happened to be not so special.

For example, public Telegram Bot API has this from field. Stackoverflow question about this for reference

[samuelcolvin]

Yes please, PR welcome.

[samuelcolvin]

No problem, surely

def dict(self, *args, **kwargs):
    d = super().dict(*args, **kwargs)
    d['from'] = d.pop('from_')
    return d

Would be simpler.

Note, this is no longer necessary, since dict() now has the by_alias argument.

[shuvozula]

For folks not using .dict(by_alias=True) , use the allow_population_by_field_name = True property (earlier was called allow_population_by_alias) in your Pydantic model: Source. So for the above code-sample, your model would look like:

class Foobar(BaseModel):
    from_: date

    class Config:
        allow_population_by_field_name = True
        fields = {
            'from_': 'from'
        }

[samuelcolvin]

I don't understand the question.