Restore loading model from buffer. (#5360) (#5366)

python-package/xgboost/core.py

@@ -1052,7 +1052,7 @@ class Booster(object):
             _check_call(
                 _LIB.XGBoosterUnserializeFromBuffer(self.handle, ptr, length))
             self.__dict__.update(state)
-        elif isinstance(model_file, (STRING_TYPES, os_PathLike)):
+        elif isinstance(model_file, (STRING_TYPES, os_PathLike, bytearray)):
             self.load_model(model_file)
         elif model_file is None:
             pass
@@ -1512,7 +1512,8 @@ class Booster(object):
         return ctypes2buffer(cptr, length.value)
 
     def load_model(self, fname):
-        """Load the model from a file, local or as URI.
+        """Load the model from a file or bytearray. Path to file can be local
+        or as an URI.
 
         The model is loaded from an XGBoost format which is universal among the
         various XGBoost interfaces. Auxiliary attributes of the Python Booster
@@ -1530,6 +1531,12 @@ class Booster(object):
             # from URL.
             _check_call(_LIB.XGBoosterLoadModel(
                 self.handle, c_str(os_fspath(fname))))
+        elif isinstance(fname, bytearray):
+            buf = fname
+            length = c_bst_ulong(len(buf))
+            ptr = (ctypes.c_char * len(buf)).from_buffer(buf)
+            _check_call(_LIB.XGBoosterLoadModelFromBuffer(self.handle, ptr,
+                                                          length))
         else:
             raise TypeError('Unknown file type: ', fname)