Django/venv/lib/python3.7/site-packages/django/db/__init__.py

from django.core import signals
from django.db.utils import (
    DEFAULT_DB_ALIAS, DJANGO_VERSION_PICKLE_KEY, ConnectionHandler,
    ConnectionRouter, DatabaseError, DataError, Error, IntegrityError,
    InterfaceError, InternalError, NotSupportedError, OperationalError,
    ProgrammingError,
)

__all__ = [
    'connection', 'connections', 'router', 'DatabaseError', 'IntegrityError',
    'InternalError', 'ProgrammingError', 'DataError', 'NotSupportedError',
    'Error', 'InterfaceError', 'OperationalError', 'DEFAULT_DB_ALIAS',
    'DJANGO_VERSION_PICKLE_KEY',
]

connections = ConnectionHandler()

router = ConnectionRouter()


class DefaultConnectionProxy:
    """
    Proxy for accessing the default DatabaseWrapper object's attributes. If you
    need to access the DatabaseWrapper object itself, use
    connections[DEFAULT_DB_ALIAS] instead.
    """
    def __getattr__(self, item):
        return getattr(connections[DEFAULT_DB_ALIAS], item)

    def __setattr__(self, name, value):
        return setattr(connections[DEFAULT_DB_ALIAS], name, value)

    def __delattr__(self, name):
        return delattr(connections[DEFAULT_DB_ALIAS], name)

    def __eq__(self, other):
        return connections[DEFAULT_DB_ALIAS] == other


# For backwards compatibility. Prefer connections['default'] instead.
connection = DefaultConnectionProxy()


# Register an event to reset saved queries when a Django request is started.
def reset_queries(**kwargs):
    for conn in connections.all():
        conn.queries_log.clear()


signals.request_started.connect(reset_queries)


# Register an event to reset transaction state and close connections past
# their lifetime.
def close_old_connections(**kwargs):
    for conn in connections.all():
        conn.close_if_unusable_or_obsolete()


signals.request_started.connect(close_old_connections)
signals.request_finished.connect(close_old_connections)