improve some type annotations

unwind/imdb_import.py

@@ -4,7 +4,7 @@ import logging
 from dataclasses import dataclass, fields
 from datetime import datetime, timezone
 from pathlib import Path
-from typing import Optional, cast
+from typing import Generator, Literal, Optional, Type, TypeVar, overload
 
 from . import config, db, request
 from .db import add_or_update_many_movies
@@ -13,6 +13,7 @@ from .models import Movie
 
 log = logging.getLogger(__name__)
 
+T = TypeVar("T")
 
 # See
 # - https://www.imdb.com/interfaces/
@@ -120,6 +121,20 @@ def count_lines(path) -> int:
     return i
 
 
+@overload
+def read_imdb_tsv(
+    path, row_type, *, unpack: Literal[False]
+) -> Generator[list[str], None, None]:
+    ...
+
+
+@overload
+def read_imdb_tsv(
+    path, row_type: Type[T], *, unpack: Literal[True] = True
+) -> Generator[T, None, None]:
+    ...
+
+
 def read_imdb_tsv(path, row_type, *, unpack=True):
     with gzip.open(path, "rt", newline="") as f:
         rows = csv.reader(f, delimiter="\t", quoting=csv.QUOTE_NONE)
@@ -158,7 +173,6 @@ def read_ratings(path):
 def read_ratings_as_mapping(path):
     """Optimized function to quickly load all ratings."""
     rows = read_imdb_tsv(path, RatingRow, unpack=False)
-    rows = cast(list[list[str]], rows)
     return {r[0]: (round(100 * (float(r[1]) - 1) / 9), int(r[2])) for r in rows}
 
 

unwind/models.py

@@ -16,6 +16,8 @@ from typing import (
 
 from .types import ULID
 
+T = TypeVar("T")
+
 
 def annotations(tp: Type) -> Optional[tuple]:
     return tp.__metadata__ if hasattr(tp, "__metadata__") else None
@@ -102,7 +104,7 @@ def asplain(o, *, fields_: set = None) -> dict[str, Any]:
     return d
 
 
-def fromplain(cls, d: dict[str, Any]):
+def fromplain(cls: Type[T], d: dict[str, Any]) -> T:
     dd = {}
     for f in fields(cls):
 
@@ -232,7 +234,6 @@ class Movie:
         self._is_lazy = False
 
 
-T = TypeVar("T")
 _RelationSentinel = object()
 """Mark a model field as containing external data.