[python-package] Add superfluous-else-raise (RET506) rule to Ruff (#6904)

* [python-package] Add superfluous-else-raise rule to ruff lint configuration

* [python-package] Fix code to follow superfluous-else-raise rule

* [python-package] Move RET506 after RET504 to maintain alphabetical order and add source rule set comment

* [python-package] Revert unintended change to preserve original formatting

docs/conf.py

@@ -254,7 +254,6 @@ def generate_doxygen_xml(app: Sphinx) -> None:
         output = "\n".join([i.decode("utf-8") for i in (stdout, stderr) if i is not None])
         if process.returncode != 0:
             raise RuntimeError(output)
-        else:
         print(output)
     except BaseException as e:
         raise Exception(f"An error has occurred while executing Doxygen\n{e}")
@@ -303,7 +302,6 @@ def generate_r_docs(app: Sphinx) -> None:
         output = "\n".join([i for i in (stdout, stderr) if i is not None])
         if process.returncode != 0:
             raise RuntimeError(output)
-        else:
         print(output)
         print("Done building R-package documentation")
     except BaseException as e:

python-package/lightgbm/basic.py

@@ -1130,7 +1130,7 @@ class _InnerPredictor:
         """
         if isinstance(data, Dataset):
             raise TypeError("Cannot use Dataset instance for prediction, please use raw data instead")
-        elif isinstance(data, pd_DataFrame) and validate_features:
+        if isinstance(data, pd_DataFrame) and validate_features:
             data_names = [str(x) for x in data.columns]
             ptr_names = (ctypes.c_char_p * len(data_names))()
             ptr_names[:] = [x.encode("utf-8") for x in data_names]
@@ -5097,7 +5097,6 @@ class Booster:
                 if split_feature == feature:
                     if isinstance(root["threshold"], str):
                         raise LightGBMError("Cannot compute split value histogram for the categorical feature")
-                    else:
                     values.append(root["threshold"])
                 add(root["left_child"])
                 add(root["right_child"])

python-package/lightgbm/sklearn.py

@@ -1761,9 +1761,9 @@ class LGBMRanker(LGBMModel):
         if eval_set is not None:
             if eval_group is None:
                 raise ValueError("Eval_group cannot be None when eval_set is not None")
-            elif len(eval_group) != len(eval_set):
+            if len(eval_group) != len(eval_set):
                 raise ValueError("Length of eval_group should be equal to eval_set")
-            elif (
+            if (
                 isinstance(eval_group, dict)
                 and any(i not in eval_group or eval_group[i] is None for i in range(len(eval_group)))
                 or isinstance(eval_group, list)

python-package/pyproject.toml

@@ -157,6 +157,8 @@ select = [
     "PL",
     # flake8-return: unnecessary assignment before return
     "RET504",
+    # flake8-return: superfluous-else-raise
+    "RET506",
     # flake8-simplify: use dict.get() instead of an if-else block
     "SIM401",
     # flake8-print