Compatibilty with python3.9

Author: theseal

src/pyff/resource.py

@@ -13,7 +13,7 @@
 from datetime import datetime
 from enum import Enum
 from threading import Condition, Lock
-from typing import TYPE_CHECKING, Any, Callable
+from typing import TYPE_CHECKING, Any, Callable, Optional
 from urllib.parse import quote as urlescape
 
 import requests
@@ -160,7 +160,7 @@ def i_handle(self, t: Resource, url=None, response=None, exception=None, last_fe
 class ResourceOpts(BaseModel):
     alias: str | None = Field(None, alias='as')  # TODO: Rename to 'name'?
     # a certificate (file) or a SHA1 fingerprint to use for signature verification
-    verify: list[str] = []
+    verify: Optional[list[str]] = None
     # TODO: move classes to make the correct typing work: Iterable[Union[Lambda, PipelineCallback]] = Field([])
     via: list[Callable] = Field([])
     # A list of callbacks that can be used to pre-process parsed metadata before validation. Use as a clue-bat.

src/pyff/utils.py

@@ -263,8 +263,8 @@ def redis():
     return thread_data.redis
 
 
-def check_signature(t: ElementTree, keys: list = [], only_one_signature: bool = False) -> ElementTree:
-    if len(keys) != 0:
+def check_signature(t: ElementTree, keys: Optional[list[str]] = None, only_one_signature: bool = False) -> ElementTree:
+    if keys:
         refs = []
         for key in keys:
             log.debug(f"verifying signature using {key}")