# documentação Django 2.0.8

# Código fonte para django.contrib.postgres.validators

    import copy

    from django.core.exceptions import ValidationError
    from django.core.validators import (
        MaxLengthValidator, MaxValueValidator, MinLengthValidator,
        MinValueValidator,
    )
    from django.utils.deconstruct import deconstructible
    from django.utils.translation import gettext_lazy as _, ngettext_lazy

    class ArrayMaxLengthValidator(MaxLengthValidator):
        message = ngettext_lazy(
            'List contains %(show_value)d item, it should contain no more than %(limit_value)d.',
            'List contains %(show_value)d items, it should contain no more than %(limit_value)d.',
            'limit_value')

    class ArrayMinLengthValidator(MinLengthValidator):
        message = ngettext_lazy(
            'List contains %(show_value)d item, it should contain no fewer than %(limit_value)d.',
            'List contains %(show_value)d items, it should contain no fewer than %(limit_value)d.',
            'limit_value')

    @deconstructible
    class KeysValidator:
        """A validator designed for HStore to require/restrict keys."""

        messages = {
            'missing_keys': _('Some keys were missing: %(keys)s'),
            'extra_keys': _('Some unknown keys were provided: %(keys)s'),
        }
        strict = False

        def __init__(self, keys, strict=False, messages=None):
            self.keys = set(keys)
            self.strict = strict
            if messages is not None:
                self.messages = copy.copy(self.messages)
                self.messages.update(messages)

        def __call__(self, value):
            keys = set(value)
            missing_keys = self.keys - keys
            if missing_keys:
                raise ValidationError(
                    self.messages['missing_keys'],
                    code='missing_keys',
                    params={'keys': ', '.join(missing_keys)},
                )
            if self.strict:
                extra_keys = keys - self.keys
                if extra_keys:
                    raise ValidationError(
                        self.messages['extra_keys'],
                        code='extra_keys',
                        params={'keys': ', '.join(extra_keys)},
                    )

        def __eq__(self, other):
            return (
                isinstance(other, self.__class__) and
                self.keys == other.keys and
                self.messages == other.messages and
                self.strict == other.strict
            )

    class RangeMaxValueValidator(MaxValueValidator):
        def compare(self, a, b):
            return a.upper > b
        message = _('Ensure that this range is completely less than or equal to %(limit_value)s.')

    class RangeMinValueValidator(MinValueValidator):
        def compare(self, a, b):
            return a.lower < b
        message = _('Ensure that this range is completely greater than or equal to %(limit_value)s.')