Default to using McBackend

pymc-devs · Feb 20, 2023 · 0b425f5 · 0b425f5
1 parent b587f7b
commit 0b425f5
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/pymc/backends/__init__.py b/pymc/backends/__init__.py
@@ -73,7 +73,7 @@
 
 HAS_MCB = False
 try:
-    from mcbackend import Backend
+    from mcbackend import Backend, NumPyBackend
 
     from pymc.backends.mcbackend import init_chain_adapters
 
@@ -119,6 +119,8 @@ def init_traces(
     model: Model,
 ) -> Sequence[IBaseTrace]:
     """Initializes a trace recorder for each chain."""
+    if HAS_MCB and backend is None:
+        backend = NumPyBackend(preallocate=expected_length)
     if HAS_MCB and isinstance(backend, Backend):
         return init_chain_adapters(
             backend=backend,