How to use the typesystem.fields.Field function in typesystem

def validate(self, value: typing.Any, *, strict: bool = False) -> typing.Any:
        if value is None and self.allow_null:
            return None
        elif value is None:
            raise self.validation_error("null")
        elif value not in Uniqueness([key for key, value in self.choices]):
            if value == "":
                if self.allow_null and not strict:
                    return None
                raise self.validation_error("required")
            raise self.validation_error("choice")
        return value


class Object(Field):
    errors = {
        "type": "Must be an object.",
        "null": "May not be null.",
        "invalid_key": "All object keys must be strings.",
        "required": "This field is required.",
        "invalid_property": "Invalid property name.",
        "empty": "Must not be empty.",
        "max_properties": "Must have no more than {max_properties} properties.",
        "min_properties": "Must have at least {min_properties} properties.",
    }

    def __init__(
        self,
        *,
        properties: typing.Dict[str, Field] = None,
        pattern_properties: typing.Dict[str, Field] = None,

if isinstance(value, str):
                value = value.lower()

            if self.allow_null and value in self.coerce_null_values:
                return None

            try:
                value = self.coerce_values[value]
            except (KeyError, TypeError):
                raise self.validation_error("type")

        return value


class Choice(Field):
    errors = {
        "null": "May not be null.",
        "required": "This field is required.",
        "choice": "Not a valid choice.",
    }

    def __init__(
        self,
        *,
        choices: typing.Sequence[typing.Union[str, typing.Tuple[str, str]]] = None,
        **kwargs: typing.Any,
    ) -> None:
        super().__init__(**kwargs)
        self.choices = [
            (choice if isinstance(choice, (tuple, list)) else (choice, choice))
            for choice in choices or []

def __or__(self, other: "Field") -> "Union":
        if isinstance(self, Union):
            any_of = self.any_of
        else:
            any_of = [self]

        if isinstance(other, Union):
            any_of += other.any_of
        else:
            any_of += [other]

        return Union(any_of=any_of)


class String(Field):
    errors = {
        "type": "Must be a string.",
        "null": "May not be null.",
        "blank": "Must not be blank.",
        "max_length": "Must have no more than {max_length} characters.",
        "min_length": "Must have at least {min_length} characters.",
        "pattern": "Must match the pattern /{pattern}/.",
        "format": "Must be a valid {format}.",
    }

    def __init__(
        self,
        *,
        allow_blank: bool = False,
        trim_whitespace: bool = True,
        max_length: int = None,

self.choice_items = [(choice, choice) for choice in choices]
        else:
            self.choice_items = list(choices)
        self.choice_dict = dict(self.choice_items)

    def validate_value(self, value, strict=False):
        if value is None and self.allow_null:
            return None
        elif value is None:
            return self.error("null")
        elif value not in self.choice_dict:
            return self.error("choice")
        return value


class Object(Field):
    errors = {
        "type": "Must be an object.",
        "null": "May not be null.",
        "invalid_key": "All object keys must be strings.",
        "required": "This field is required.",
        "invalid_property": "Invalid property name.",
        "empty": "Must not be empty.",
        "max_properties": "Must have no more than {max_properties} properties.",
        "min_properties": "Must have at least {min_properties} properties.",
    }

    def __init__(
        self,
        properties=None,
        pattern_properties=None,
        additional_properties=True,

class Date(String):
    def __init__(self, **kwargs: typing.Any) -> None:
        super().__init__(format="date", **kwargs)


class Time(String):
    def __init__(self, **kwargs: typing.Any) -> None:
        super().__init__(format="time", **kwargs)


class DateTime(String):
    def __init__(self, **kwargs: typing.Any) -> None:
        super().__init__(format="datetime", **kwargs)


class Union(Field):
    errors = {"null": "May not be null.", "union": "Did not match any valid type."}

    def __init__(self, any_of: typing.List[Field], **kwargs: typing.Any):
        super().__init__(**kwargs)

        self.any_of = any_of
        if any([child.allow_null for child in any_of]):
            self.allow_null = True

    def validate(self, value: typing.Any, strict: bool = False) -> typing.Any:
        if value is None and self.allow_null:
            return None
        elif value is None:
            raise self.validation_error("null")

        candidate_errors = []

class Integer(Number):
    numeric_type = int


class Float(Number):
    numeric_type = float


class Decimal(Number):
    numeric_type = decimal.Decimal

    def serialize(self, obj: typing.Any) -> typing.Any:
        return None if obj is None else float(obj)


class Boolean(Field):
    errors = {"type": "Must be a boolean.", "null": "May not be null."}
    coerce_values = {
        "true": True,
        "false": False,
        "on": True,
        "off": False,
        "1": True,
        "0": False,
        "": False,
        1: True,
        0: False,
    }
    coerce_null_values = {"", "null", "none"}

    def validate(self, value: typing.Any, *, strict: bool = False) -> typing.Any:
        if value is None and self.allow_null:

messages = error.messages()
                if (
                    len(messages) != 1
                    or messages[0].code != "type"
                    or messages[0].index
                ):
                    candidate_errors.append(error)

        if len(candidate_errors) == 1:
            # If exactly one child was of the correct type, then we can use
            # the error from the child.
            raise candidate_errors[0]
        raise self.validation_error("union")


class Any(Field):
    """
    Always matches.
    """

    def validate(self, value: typing.Any, strict: bool = False) -> typing.Any:
        return value


class Const(Field):
    """
    Only ever matches the given given value.
    """

    errors = {"only_null": "Must be null.", "const": "Must be the value '{const}'."}

    def __init__(self, const: typing.Any, **kwargs: typing.Any):

for key, value in pattern_properties.items()
            }

        additional_properties = data.get("additionalProperties", None)
        if additional_properties is None:
            additional_properties_argument: typing.Union[None, bool, Field] = (None)
        elif isinstance(additional_properties, bool):
            additional_properties_argument = additional_properties
        else:
            additional_properties_argument = from_json_schema(
                additional_properties, definitions=definitions
            )

        property_names = data.get("propertyNames", None)
        if property_names is None:
            property_names_argument: typing.Optional[Field] = None
        else:
            property_names_argument = from_json_schema(
                property_names, definitions=definitions
            )

        kwargs = {
            "allow_null": allow_null,
            "properties": properties_argument,
            "pattern_properties": pattern_properties_argument,
            "additional_properties": additional_properties_argument,
            "property_names": property_names_argument,
            "min_properties": data.get("minProperties", None),
            "max_properties": data.get("maxProperties", None),
            "required": data.get("required", None),
            "default": data.get("default", NO_DEFAULT),
        }

# The following fields are required for complete JSON schema support,
# but are undocumented as we don't recommend using them directly.
import typing

from typesystem.fields import Any, Field


class NeverMatch(Field):
    """
    Doesn't ever match.
    """

    errors = {"never": "This never validates."}

    def __init__(self, **kwargs: typing.Any) -> None:
        assert "allow_null" not in kwargs
        super().__init__(**kwargs)

    def validate(self, value: typing.Any, strict: bool = False) -> typing.Any:
        raise self.validation_error("never")


class OneOf(Field):
    """

"min_length": min_length if min_length > 1 else None,
            "max_length": data.get("maxLength", None),
            "format": data.get("format"),
            "pattern": data.get("pattern", None),
            "default": data.get("default", NO_DEFAULT),
        }
        return String(**kwargs)

    elif type_string == "boolean":
        kwargs = {"allow_null": allow_null, "default": data.get("default", NO_DEFAULT)}
        return Boolean(**kwargs)

    elif type_string == "array":
        items = data.get("items", None)
        if items is None:
            items_argument: typing.Union[None, Field, typing.List[Field]] = None
        elif isinstance(items, list):
            items_argument = [
                from_json_schema(item, definitions=definitions) for item in items
            ]
        else:
            items_argument = from_json_schema(items, definitions=definitions)

        additional_items = data.get("additionalItems", None)
        if additional_items is None:
            additional_items_argument: typing.Union[bool, Field] = True
        elif isinstance(additional_items, bool):
            additional_items_argument = additional_items
        else:
            additional_items_argument = from_json_schema(
                additional_items, definitions=definitions
            )