LearningSolver: Keep original H5 file unmodified

miplearn/solvers/learning.py

@@ -8,6 +8,7 @@ from typing import List, Any, Union, Dict, Callable, Optional
 from miplearn.h5 import H5File
 from miplearn.io import _to_h5_filename
 from miplearn.solvers.abstract import AbstractModel
+import shutil
 
 
 class LearningSolver:
@@ -25,15 +26,20 @@ class LearningSolver:
         model: Union[str, AbstractModel],
         build_model: Optional[Callable] = None,
     ) -> Dict[str, Any]:
+        h5_filename, mode = NamedTemporaryFile().name, "w"
         if isinstance(model, str):
-            h5_filename = _to_h5_filename(model)
             assert build_model is not None
+            old_h5_filename = _to_h5_filename(model)
             model = build_model(model)
             assert isinstance(model, AbstractModel)
-        else:
-            h5_filename = NamedTemporaryFile().name
+
+            # If the instance has an associate H5 file, we make a temporary copy of it,
+            # then work on that copy. We keep the original file unmodified
+            if exists(old_h5_filename):
+                shutil.copy(old_h5_filename, h5_filename)
+                mode = "r+"
+
         stats: Dict[str, Any] = {}
-        mode = "r+" if exists(h5_filename) else "w"
         with H5File(h5_filename, mode) as h5:
             model.extract_after_load(h5)
             if not self.skip_lp: