From 71b6550f11b557ab3626ff906cde3cfc340c09c2 Mon Sep 17 00:00:00 2001
From: James Lamb <jaylamb20@gmail.com>
Date: Mon, 29 Aug 2022 21:11:33 -0400
Subject: [PATCH] [python-package] add type hints on empty initializations
 (#5445)

---
 python-package/lightgbm/basic.py  | 6 +++---
 python-package/lightgbm/engine.py | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/python-package/lightgbm/basic.py b/python-package/lightgbm/basic.py
index bb707f61f07e..3004b95eaac1 100644
--- a/python-package/lightgbm/basic.py
+++ b/python-package/lightgbm/basic.py
@@ -2514,7 +2514,7 @@ def get_ref_chain(self, ref_limit: int = 100) -> Set["Dataset"]:
             Chain of references of the Datasets.
         """
         head = self
-        ref_chain = set()
+        ref_chain: Set[Dataset] = set()
         while len(ref_chain) < ref_limit:
             if isinstance(head, Dataset):
                 ref_chain.add(head)
@@ -2733,8 +2733,8 @@ def __init__(
                 ctypes.byref(self.handle)))
             # save reference to data
             self.train_set = train_set
-            self.valid_sets = []
-            self.name_valid_sets = []
+            self.valid_sets: List[Dataset] = []
+            self.name_valid_sets: List[str] = []
             self.__num_dataset = 1
             self.__init_predictor = train_set._predictor
             if self.__init_predictor is not None:
diff --git a/python-package/lightgbm/engine.py b/python-package/lightgbm/engine.py
index 2cc050362d35..71e761ccf067 100644
--- a/python-package/lightgbm/engine.py
+++ b/python-package/lightgbm/engine.py
@@ -300,7 +300,7 @@ def __init__(
         model_file : str, pathlib.Path or None, optional (default=None)
             Path to the CVBooster model file.
         """
-        self.boosters = []
+        self.boosters: List[Booster] = []
         self.best_iteration = -1
 
         if model_file is not None: