fix: use deepcopy when dumping mixed types

dpdata/deepmd/mixed.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import copy
 import glob
 import os
 import shutil
@@ -160,6 +161,9 @@ def dump(folder, data, set_size=2000, comp_prec=np.float32, remove_sets=True):
     if "real_atom_types" not in data:
         from dpdata import LabeledSystem, System
 
+        # not change the original content
+        data = copy.deepcopy(data)
+
         if "energies" in data:
             temp_sys = LabeledSystem(data=data)
         else:

tests/test_deepmd_mixed.py

@@ -314,5 +314,27 @@ def test_str(self):
         )
 
 
+class TestMixedSingleSystemsDump(unittest.TestCase, CompLabeledSys, IsNoPBC):
+    def setUp(self):
+        self.places = 6
+        self.e_places = 6
+        self.f_places = 6
+        self.v_places = 6
+
+        # C1H4
+        self.system_1 = dpdata.LabeledSystem(
+            "gaussian/methane.gaussianlog", fmt="gaussian/log"
+        )
+        self.system_2 = dpdata.LabeledSystem(
+            "gaussian/methane.gaussianlog", fmt="gaussian/log"
+        )
+        # test dump
+        self.system_1.to("deepmd/npy/mixed", "tmp.deepmd.mixed.single")
+
+    def tearDown(self):
+        if os.path.exists("tmp.deepmd.mixed.single"):
+            shutil.rmtree("tmp.deepmd.mixed.single")
+
+
 if __name__ == "__main__":
     unittest.main()