Merge pull request #4135 from yuhldr/develop

pylammps small changes and bugfixes

python/lammps/pylammps.py

@@ -196,7 +196,7 @@ class Atom(object):
 
     :type: float
     """
-    return self.get("mass", self.index)
+    return self.get("mass", self.type)
 
   @property
   def radius(self):
@@ -532,6 +532,18 @@ class PyLammps(object):
     """
     self._cmd_history = []
 
+
+  def append_cmd_history(self, cmd):
+    """
+    Commands will be added to the command history but not executed.
+
+    Add `commands` only to the command history, but do not execute them, so that you can
+    conveniently create Lammps input files, using
+    :py:meth:`PyLammps.write_script()`.
+    """
+    self._cmd_history.append(cmd)
+
+
   def command(self, cmd):
     """
     Execute LAMMPS command