explicit default template context through get method

cashews/key_context.py

@@ -7,8 +7,8 @@
 from typing import Any
 
 _REWRITE = "__rewrite"
-_template_context: ContextVar[dict[str, Any]] = ContextVar("template_context")
-_template_context.set({_REWRITE: False})
+TContext = dict[str, Any]
+_template_context: ContextVar[TContext | None] = ContextVar("template_context", default=None)
 _empty = object()
 
 
@@ -22,25 +22,28 @@ def context(rewrite=_empty, **values) -> Iterator[None]:
         )
     else:
         rewrite = False
-    new_context = {**_template_context.get(), **values}
-    new_context[_REWRITE] = rewrite
+    new_context = {**_get_raw(), **values, _REWRITE: rewrite}
     token = _template_context.set(new_context)
     try:
         yield
     finally:
         _template_context.reset(token)
 
 
-def get() -> tuple[dict[str, Any], bool]:
-    _context = {**_template_context.get()}
+def get() -> tuple[TContext, bool]:
+    _context = {**_get_raw()}  # a copy
     return _context, _context.pop(_REWRITE)
 
 
+def _get_raw() -> TContext:
+    return _template_context.get() or {_REWRITE: False}
+
+
 def register(*names: str) -> None:
     warnings.warn(
         "`register_key_context` deprecated and will be removed in next release, use @ notation",
         DeprecationWarning,
         stacklevel=2,
     )
     new_names = dict.fromkeys(names, "")
-    _template_context.set({**new_names, **_template_context.get()})
+    _template_context.set({**new_names, **_get_raw()})

tests/test_bugs.py

@@ -0,0 +1,17 @@
+import asyncio
+
+from cashews import Cache
+
+
+async def test_issue_382():
+    cache = Cache()
+    cache.setup("mem://")
+
+    @cache(ttl=60, key="item:{item_id}")
+    async def get_item(item_id: int):
+        return f"item_{item_id}"
+
+    def sync_get_item(item_id: int):
+        return asyncio.run(get_item(item_id))
+
+    await asyncio.get_running_loop().run_in_executor(None, sync_get_item, 123)