Some better type hints on FileCacher / LargeObject

Use typing.IO[bytes] instead of BinaryIO, because some stdlib types are
apparently only compatible with the former.

Author: prandla

cms/db/base.py

@@ -74,7 +74,7 @@ def sa_mapper(self):
         return object_mapper(self)
 
     @property
-    def sa_session(self):
+    def sa_session(self) -> Session:
         return object_session(self)
 
     @property

cms/db/filecacher.py

@@ -90,7 +90,7 @@ class FileCacherBackend(metaclass=ABCMeta):
     """
 
     @abstractmethod
-    def get_file(self, digest: str) -> typing.BinaryIO:
+    def get_file(self, digest: str) -> typing.IO[bytes]:
         """Retrieve a file from the storage.
 
         digest: the digest of the file to retrieve.
@@ -104,7 +104,7 @@ def get_file(self, digest: str) -> typing.BinaryIO:
         pass
 
     @abstractmethod
-    def create_file(self, digest: str) -> typing.BinaryIO | None:
+    def create_file(self, digest: str) -> typing.IO[bytes] | None:
         """Create an empty file that will live in the storage.
 
         Once the caller has written the contents to the file, the commit_file()
@@ -120,7 +120,7 @@ def create_file(self, digest: str) -> typing.BinaryIO | None:
         pass
 
     @abstractmethod
-    def commit_file(self, fobj: typing.BinaryIO, digest: str, desc: str = "") -> bool:
+    def commit_file(self, fobj: typing.IO[bytes], digest: str, desc: str = "") -> bool:
         """Commit a file created by create_file() to be stored.
 
         Given a file object returned by create_file(), this function populates
@@ -238,7 +238,6 @@ def create_file(self, digest):
             return None
 
         # Create a temporary file in the same directory
-        temp_file: typing.BinaryIO
         temp_file = tempfile.NamedTemporaryFile('wb', delete=False,
                                                 prefix=".tmp.",
                                                 suffix=digest,
@@ -305,11 +304,6 @@ def list(self):
         return list((x, "") for x in os.listdir(self.path))
 
 
-# this class has type-checking errors because our LargeObject type is not
-# compatible with typing.BinaryIO, despite being a valid IO object in practice.
-# This is mostly due to Python's IO types being difficult to handle statically.
-# Anyways, it should be fine to pretend that the values returned here are
-# typing.BinaryIO.
 class DBBackend(FileCacherBackend):
     """This class implements an actual backend for FileCacher that
     stores the files as lobjects (encapsuled in a FSObject) into a
@@ -589,7 +583,7 @@ def precache_lock(self) -> io.TextIOBase | None:
             if not returned:
                 fobj.close()
 
-    def _load(self, digest: str, cache_only: bool) -> typing.BinaryIO | None:
+    def _load(self, digest: str, cache_only: bool) -> typing.IO[bytes] | None:
         """Load a file into the cache and open it for reading.
 
         cache_only: don't open the file for reading.
@@ -657,7 +651,7 @@ def cache_file(self, digest: str):
 
         self._load(digest, True)
 
-    def get_file(self, digest: str) -> typing.BinaryIO:
+    def get_file(self, digest: str) -> typing.IO[bytes]:
         """Retrieve a file from the storage.
 
         If it's available in the cache use that copy, without querying
@@ -703,7 +697,7 @@ def get_file_content(self, digest: str) -> bytes:
         with self.get_file(digest) as src:
             return src.read()
 
-    def get_file_to_fobj(self, digest: str, dst: typing.BinaryIO):
+    def get_file_to_fobj(self, digest: str, dst: typing.IO[bytes]):
         """Retrieve a file from the storage.
 
         See `get_file'. This method will write the content of the file
@@ -741,7 +735,7 @@ def get_file_to_path(self, digest: str, dst_path: str):
             with open(dst_path, 'wb') as dst:
                 copyfileobj(src, dst, self.CHUNK_SIZE)
 
-    def put_file_from_fobj(self, src: typing.BinaryIO, desc: str = "") -> str:
+    def put_file_from_fobj(self, src: typing.IO[bytes], desc: str = "") -> str:
         """Store a file in the storage.
 
         If it's already (for some reason...) in the cache send that

cms/db/fsobject.py

@@ -37,7 +37,7 @@
 from . import Base, custom_psycopg2_connection, Session
 
 
-class LargeObject(io.RawIOBase):
+class LargeObject(io.RawIOBase, typing.BinaryIO):
 
     """Present a PostgreSQL large object as a Python file-object.
 
@@ -119,7 +119,13 @@ def __init__(self, loid: int, mode: str = 'rb'):
         cursor.close()
 
     # cursor is typed as typing.Any because psycopg2 doesn't have good type hints.
-    def _execute(self, operation: str, parameters: dict[str, typing.Any], message: str, cursor: typing.Any | None = None) -> typing.Any:
+    def _execute(
+        self,
+        operation: str,
+        parameters: dict[str, typing.Any],
+        message: str,
+        cursor: typing.Any | None = None
+    ) -> typing.Any:
         """Run the given query making many success checks.
 
         Execute the given SQL statement, instantiated with the given
@@ -403,7 +409,7 @@ def delete(self):
         self.sa_session.delete(self)
 
     @classmethod
-    def get_from_digest(cls, digest: str, session: Session) -> Self:
+    def get_from_digest(cls, digest: str, session: Session) -> Self | None:
         """Return the FSObject with the specified digest, using the
         specified session.