From efe651e3bae7a279b60cda151b4bedf31e605bd6 Mon Sep 17 00:00:00 2001
From: Francesco Zanetta <62377868+frazane@users.noreply.github.com>
Date: Wed, 23 Oct 2024 18:23:07 +0200
Subject: [PATCH] use torch.as_tensor to preserve gradients (#79)

---
 scoringrules/backend/registry.py | 8 +++-----
 scoringrules/backend/torch.py    | 3 ++-
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/scoringrules/backend/registry.py b/scoringrules/backend/registry.py
index 3b174b6..7c4aae5 100644
--- a/scoringrules/backend/registry.py
+++ b/scoringrules/backend/registry.py
@@ -59,11 +59,9 @@ def __getitem__(self, __key: str) -> ArrayBackend:
         """Get a backend from the registry."""
         try:
             return super().__getitem__(__key)
-        except KeyError as err:
-            raise BackendNotRegistered(
-                f"The backend '{__key}' is not registered. "
-                f"You can register it with scoringrules.register_backend('{__key}')"
-            ) from err
+        except KeyError:
+            self.register_backend(__key)
+            return super().__getitem__(__key)
 
     def set_active(self, backend: str):
         self._active = backend
diff --git a/scoringrules/backend/torch.py b/scoringrules/backend/torch.py
index eb92717..933271d 100644
--- a/scoringrules/backend/torch.py
+++ b/scoringrules/backend/torch.py
@@ -32,7 +32,8 @@ def asarray(
         *,
         dtype: Dtype | None = None,
     ) -> "Tensor":
-        return torch.asarray(obj, dtype=dtype)
+        # torch.asarray(obj) would cancel gradients!
+        return torch.as_tensor(obj, dtype=dtype)
 
     def broadcast_arrays(self, *arrays: "Tensor") -> tuple["Tensor", ...]:
         return torch.broadcast_tensors(*arrays)