add torch interop warning and actionable hint (#385)

Co-authored-by: Lilith Hafner <[email protected]>

Author: LilithHafner

pysrc/juliacall/__init__.py

@@ -53,6 +53,15 @@ def init():
     import ctypes as c
     import sys
     import subprocess
+    import warnings
+
+    # importing pytorch before juliacall sometimes causes segfaults. TODO: remove
+    if "torch" in sys.modules:
+        warnings.warn(
+            "`torch` was loaded before the juliacall. This may cause a segfault. "
+            "To avoid this, import `juliacall` *before* importing `torch`. "
+            "For updates, see https://github.com/pytorch/pytorch/issues/78829"
+        )
 
     def option(name, default=None, xkey=None, envkey=None):
         """Get an option.