Django/venv/lib/python3.7/site-packages/django/contrib/postgres/apps.py

from psycopg2.extras import (
    DateRange, DateTimeRange, DateTimeTZRange, NumericRange,
)

from django.apps import AppConfig
from django.db import connections
from django.db.backends.signals import connection_created
from django.db.migrations.writer import MigrationWriter
from django.db.models import CharField, TextField
from django.test.signals import setting_changed
from django.utils.translation import gettext_lazy as _

from .lookups import SearchLookup, TrigramSimilar, Unaccent
from .serializers import RangeSerializer
from .signals import register_type_handlers

RANGE_TYPES = (DateRange, DateTimeRange, DateTimeTZRange, NumericRange)


def uninstall_if_needed(setting, value, enter, **kwargs):
    """
    Undo the effects of PostgresConfig.ready() when django.contrib.postgres
    is "uninstalled" by override_settings().
    """
    if not enter and setting == 'INSTALLED_APPS' and 'django.contrib.postgres' not in set(value):
        connection_created.disconnect(register_type_handlers)
        CharField._unregister_lookup(Unaccent)
        TextField._unregister_lookup(Unaccent)
        CharField._unregister_lookup(SearchLookup)
        TextField._unregister_lookup(SearchLookup)
        CharField._unregister_lookup(TrigramSimilar)
        TextField._unregister_lookup(TrigramSimilar)
        # Disconnect this receiver until the next time this app is installed
        # and ready() connects it again to prevent unnecessary processing on
        # each setting change.
        setting_changed.disconnect(uninstall_if_needed)
        MigrationWriter.unregister_serializer(RANGE_TYPES)


class PostgresConfig(AppConfig):
    name = 'django.contrib.postgres'
    verbose_name = _('PostgreSQL extensions')

    def ready(self):
        setting_changed.connect(uninstall_if_needed)
        # Connections may already exist before we are called.
        for conn in connections.all():
            if conn.vendor == 'postgresql':
                conn.introspection.data_types_reverse.update({
                    3802: 'django.contrib.postgres.fields.JSONField',
                    3904: 'django.contrib.postgres.fields.IntegerRangeField',
                    3906: 'django.contrib.postgres.fields.DecimalRangeField',
                    3910: 'django.contrib.postgres.fields.DateTimeRangeField',
                    3912: 'django.contrib.postgres.fields.DateRangeField',
                    3926: 'django.contrib.postgres.fields.BigIntegerRangeField',
                })
                if conn.connection is not None:
                    register_type_handlers(conn)
        connection_created.connect(register_type_handlers)
        CharField.register_lookup(Unaccent)
        TextField.register_lookup(Unaccent)
        CharField.register_lookup(SearchLookup)
        TextField.register_lookup(SearchLookup)
        CharField.register_lookup(TrigramSimilar)
        TextField.register_lookup(TrigramSimilar)
        MigrationWriter.register_serializer(RANGE_TYPES, RangeSerializer)