[backport] Fix pylint errors. (#7967) (#7981)

* Fix pylint errors. (#7967)

* Rebase error.

python-package/setup.py

@@ -97,7 +97,7 @@ class BuildExt(build_ext.build_ext):  # pylint: disable=too-many-ancestors
 
     logger = logging.getLogger('XGBoost build_ext')
 
-    # pylint: disable=too-many-arguments,no-self-use
+    # pylint: disable=too-many-arguments
     def build(
         self,
         src_dir: str,

python-package/xgboost/callback.py

@@ -1,5 +1,5 @@
 # coding: utf-8
-# pylint: disable=invalid-name, too-many-statements, no-self-use
+# pylint: disable=invalid-name, too-many-statements
 # pylint: disable=too-many-arguments
 """Callback library containing training routines.  See :doc:`Callback Functions
 </python/callbacks>` for a quick introduction.

python-package/xgboost/core.py

@@ -3,6 +3,7 @@
 """Core XGBoost Library."""
 from abc import ABC, abstractmethod
 from collections.abc import Mapping
+import copy
 from typing import List, Optional, Any, Union, Dict, TypeVar
 from typing import Callable, Tuple, cast, Sequence, Type, Iterable
 import ctypes
@@ -1577,7 +1578,7 @@ def copy(self) -> "Booster":
         booster: `Booster`
             a copied booster model
         """
-        return self.__copy__()
+        return copy.copy(self)
 
     def attr(self, key: str) -> Optional[str]:
         """Get attribute string from the Booster.
@@ -2309,15 +2310,15 @@ def dump_model(self, fout: Union[str, os.PathLike], fmap: Union[str, os.PathLike
         ret = self.get_dump(fmap, with_stats, dump_format)
         if dump_format == 'json':
             fout_obj.write('[\n')
-            for i, _ in enumerate(ret):
-                fout_obj.write(ret[i])
+            for i, val in enumerate(ret):
+                fout_obj.write(val)
                 if i < len(ret) - 1:
                     fout_obj.write(",\n")
             fout_obj.write('\n]')
         else:
-            for i, _ in enumerate(ret):
+            for i, val in enumerate(ret):
                 fout_obj.write(f"booster[{i}]:\n")
-                fout_obj.write(ret[i])
+                fout_obj.write(val)
         if need_close:
             fout_obj.close()
 
@@ -2604,8 +2605,8 @@ def get_split_value_histogram(
         values = []
         # pylint: disable=consider-using-f-string
         regexp = re.compile(r"\[{0}<([\d.Ee+-]+)\]".format(feature))
-        for i, _ in enumerate(xgdump):
-            m = re.findall(regexp, xgdump[i])
+        for i, val in enumerate(xgdump):
+            m = re.findall(regexp, val)
             values.extend([float(x) for x in m])
 
         n_unique = len(np.unique(values))

python-package/xgboost/dask.py

@@ -1721,7 +1721,7 @@ def _client_sync(self, func: Callable, **kwargs: Any) -> Any:
     """Implementation of the Scikit-Learn API for XGBoost.""", ["estimators", "model"]
 )
 class DaskXGBRegressor(DaskScikitLearnBase, XGBRegressorBase):
-    # pylint: disable=missing-class-docstring
+    """dummy doc string to workaround pylint, replaced by the decorator."""
     async def _fit_async(
         self,
         X: _DaskCollection,

python-package/xgboost/data.py

@@ -2,7 +2,6 @@
 # pylint: disable=too-many-return-statements, import-error
 '''Data dispatching for DMatrix.'''
 import ctypes
-from distutils import version
 import json
 import warnings
 import os