"""Classes and functions for cache persistence"""
# flake8: noqa: F401
from logging import getLogger
from typing import Type, Union
from .base import BaseCache, BaseStorage
# Backend-specific keyword arguments equivalent to 'cache_name'
CACHE_NAME_KWARGS = ['db_path', 'db_name', 'namespace', 'table_name']
# All backend-specific keyword arguments
BACKEND_KWARGS = CACHE_NAME_KWARGS + [
'connection',
'endpoint_url',
'fast_save',
'ignored_parameters',
'include_get_headers',
'name',
'read_capacity_units',
'region_name',
'salt',
'secret_key',
'suppress_warnings',
'write_capacity_units',
]
BackendSpecifier = Union[str, BaseCache, Type[BaseCache], None]
logger = getLogger(__name__)
[docs]def get_placeholder_backend(original_exception: Exception = None) -> Type[BaseCache]:
"""Create a placeholder type for a backend class that does not have dependencies installed.
This allows delaying ImportErrors until init time, rather than at import time.
"""
class PlaceholderBackend(BaseCache):
def __init__(*args, **kwargs):
msg = 'Dependencies are not installed for this backend'
logger.error(msg)
raise original_exception or ImportError(msg)
return PlaceholderBackend
# Import all backend classes for which dependencies are installed
try:
from .dynamodb import DynamoDbCache, DynamoDbDict
except ImportError as e:
DynamoDbCache = DynamoDbDict = get_placeholder_backend(e) # type: ignore
try:
from .gridfs import GridFSCache, GridFSPickleDict
except ImportError as e:
GridFSCache = GridFSPickleDict = get_placeholder_backend(e) # type: ignore
try:
from .mongo import MongoCache, MongoDict, MongoPickleDict
except ImportError as e:
MongoCache = MongoDict = MongoPickleDict = get_placeholder_backend(e) # type: ignore
try:
from .redis import RedisCache, RedisDict
except ImportError as e:
RedisCache = RedisDict = get_placeholder_backend(e) # type: ignore
try:
# Note: Heroku doesn't support SQLite due to ephemeral storage
from .sqlite import DbCache, DbDict, DbPickleDict
except ImportError as e:
DbCache = DbDict = DbPickleDict = get_placeholder_backend(e) # type: ignore
BACKEND_CLASSES = {
'dynamodb': DynamoDbCache,
'gridfs': GridFSCache,
'memory': BaseCache,
'mongo': MongoCache,
'redis': RedisCache,
'sqlite': DbCache,
}
[docs]def init_backend(backend: BackendSpecifier, *args, **kwargs) -> BaseCache:
"""Initialize a backend given a name, class, or instance"""
logger.debug(f'Initializing backend: {backend}')
# Omit 'cache_name' positional arg if an equivalent backend-specific kwarg is specified
if any([k in kwargs for k in CACHE_NAME_KWARGS]):
args = tuple()
# Determine backend class
if isinstance(backend, BaseCache):
return backend
elif isinstance(backend, type):
return backend(*args, **kwargs)
elif not backend:
backend = 'sqlite' if BACKEND_CLASSES['sqlite'] else 'memory'
backend = str(backend).lower().replace('mongodb', 'mongo')
if backend not in BACKEND_CLASSES:
raise ValueError(f'Invalid backend: {backend}. Choose from: {BACKEND_CLASSES.keys()}')
return BACKEND_CLASSES[backend](*args, **kwargs)