# documentación de Django - 1.10.7

# Código fuente para django.contrib.postgres.fields.ranges

    import json

    from psycopg2.extras import DateRange, DateTimeTZRange, NumericRange, Range

    from django.contrib.postgres import forms, lookups
    from django.db import models
    from django.utils import six

    from .utils import AttributeSetter

    __all__ = [
        'RangeField', 'IntegerRangeField', 'BigIntegerRangeField',
        'FloatRangeField', 'DateTimeRangeField', 'DateRangeField',
    ]

    class RangeField(models.Field):
        empty_strings_allowed = False

        def __init__(self, *args, **kwargs):
            # Initializing base_field here ensures that its model matches the model for self.
            if hasattr(self, 'base_field'):
                self.base_field = self.base_field()
            super(RangeField, self).__init__(*args, **kwargs)

        @property
        def model(self):
            try:
                return self.__dict__['model']
            except KeyError:
                raise AttributeError("'%s' object has no attribute 'model'" % self.__class__.__name__)

        @model.setter
        def model(self, model):
            self.__dict__['model'] = model
            self.base_field.model = model

        def get_prep_value(self, value):
            if value is None:
                return None
            elif isinstance(value, Range):
                return value
            elif isinstance(value, (list, tuple)):
                return self.range_type(value[0], value[1])
            return value

        def to_python(self, value):
            if isinstance(value, six.string_types):
                # Assume we're deserializing
                vals = json.loads(value)
                for end in ('lower', 'upper'):
                    if end in vals:
                        vals[end] = self.base_field.to_python(vals[end])
                value = self.range_type(**vals)
            elif isinstance(value, (list, tuple)):
                value = self.range_type(value[0], value[1])
            return value

        def set_attributes_from_name(self, name):
            super(RangeField, self).set_attributes_from_name(name)
            self.base_field.set_attributes_from_name(name)

        def value_to_string(self, obj):
            value = self.value_from_object(obj)
            if value is None:
                return None
            if value.isempty:
                return json.dumps({"empty": True})
            base_field = self.base_field
            result = {"bounds": value._bounds}
            for end in ('lower', 'upper'):
                val = getattr(value, end)
                if val is None:
                    result[end] = None
                else:
                    obj = AttributeSetter(base_field.attname, val)
                    result[end] = base_field.value_to_string(obj)
            return json.dumps(result)

        def formfield(self, **kwargs):
            kwargs.setdefault('form_class', self.form_field)
            return super(RangeField, self).formfield(**kwargs)

    class IntegerRangeField(RangeField):
        base_field = models.IntegerField
        range_type = NumericRange
        form_field = forms.IntegerRangeField

        def db_type(self, connection):
            return 'int4range'

    class BigIntegerRangeField(RangeField):
        base_field = models.BigIntegerField
        range_type = NumericRange
        form_field = forms.IntegerRangeField

        def db_type(self, connection):
            return 'int8range'

    class FloatRangeField(RangeField):
        base_field = models.FloatField
        range_type = NumericRange
        form_field = forms.FloatRangeField

        def db_type(self, connection):
            return 'numrange'

    class DateTimeRangeField(RangeField):
        base_field = models.DateTimeField
        range_type = DateTimeTZRange
        form_field = forms.DateTimeRangeField

        def db_type(self, connection):
            return 'tstzrange'

    class DateRangeField(RangeField):
        base_field = models.DateField
        range_type = DateRange
        form_field = forms.DateRangeField

        def db_type(self, connection):
            return 'daterange'

    RangeField.register_lookup(lookups.DataContains)
    RangeField.register_lookup(lookups.ContainedBy)
    RangeField.register_lookup(lookups.Overlap)

    class RangeContainedBy(models.Lookup):
        lookup_name = 'contained_by'
        type_mapping = {
            'integer': 'int4range',
            'bigint': 'int8range',
            'double precision': 'numrange',
            'date': 'daterange',
            'timestamp with time zone': 'tstzrange',
        }

        def as_sql(self, qn, connection):
            field = self.lhs.output_field
            if isinstance(field, models.FloatField):
                sql = '%s::numeric <@ %s::{}'.format(self.type_mapping[field.db_type(connection)])
            else:
                sql = '%s <@ %s::{}'.format(self.type_mapping[field.db_type(connection)])
            lhs, lhs_params = self.process_lhs(qn, connection)
            rhs, rhs_params = self.process_rhs(qn, connection)
            params = lhs_params + rhs_params
            return sql % (lhs, rhs), params

        def get_prep_lookup(self):
            return RangeField().get_prep_value(self.rhs)

    models.DateField.register_lookup(RangeContainedBy)
    models.DateTimeField.register_lookup(RangeContainedBy)
    models.IntegerField.register_lookup(RangeContainedBy)
    models.BigIntegerField.register_lookup(RangeContainedBy)
    models.FloatField.register_lookup(RangeContainedBy)

    @RangeField.register_lookup
    class FullyLessThan(lookups.PostgresSimpleLookup):
        lookup_name = 'fully_lt'
        operator = '<<'

    @RangeField.register_lookup
    class FullGreaterThan(lookups.PostgresSimpleLookup):
        lookup_name = 'fully_gt'
        operator = '>>'

    @RangeField.register_lookup
    class NotLessThan(lookups.PostgresSimpleLookup):
        lookup_name = 'not_lt'
        operator = '&>'

    @RangeField.register_lookup
    class NotGreaterThan(lookups.PostgresSimpleLookup):
        lookup_name = 'not_gt'
        operator = '&<'

    @RangeField.register_lookup
    class AdjacentToLookup(lookups.PostgresSimpleLookup):
        lookup_name = 'adjacent_to'
        operator = '-|-'

    @RangeField.register_lookup
    class RangeStartsWith(models.Transform):
        lookup_name = 'startswith'
        function = 'lower'

        @property
        def output_field(self):
            return self.lhs.output_field.base_field

    @RangeField.register_lookup
    class RangeEndsWith(models.Transform):
        lookup_name = 'endswith'
        function = 'upper'

        @property
        def output_field(self):
            return self.lhs.output_field.base_field

    @RangeField.register_lookup
    class IsEmpty(models.Transform):
        lookup_name = 'isempty'
        function = 'isempty'
        output_field = models.BooleanField()