Added "TODO" comments

Author: MomIsBestFriend

pandas/_libs/groupby.pyx

@@ -869,6 +869,8 @@ def group_last(rank_t[:, :] out,
 
     assert min_count == -1, "'min_count' only used in add and prod"
 
+    # TODO(cython 3.0):
+    # Instead of `labels.shape[0]` use `len(labels)`
     if not len(values) == labels.shape[0]:
         raise AssertionError("len(index) != len(labels)")
 
@@ -960,6 +962,8 @@ def group_nth(rank_t[:, :] out,
 
     assert min_count == -1, "'min_count' only used in add and prod"
 
+    # TODO(cython 3.0):
+    # Instead of `labels.shape[0]` use `len(labels)`
     if not len(values) == labels.shape[0]:
         raise AssertionError("len(index) != len(labels)")
 
@@ -1254,6 +1258,8 @@ def group_max(groupby_t[:, :] out,
 
     assert min_count == -1, "'min_count' only used in add and prod"
 
+    # TODO(cython 3.0):
+    # Instead of `labels.shape[0]` use `len(labels)`
     if not len(values) == labels.shape[0]:
         raise AssertionError("len(index) != len(labels)")
 
@@ -1327,6 +1333,8 @@ def group_min(groupby_t[:, :] out,
 
     assert min_count == -1, "'min_count' only used in add and prod"
 
+    # TODO(cython 3.0):
+    # Instead of `labels.shape[0]` use `len(labels)`
     if not len(values) == labels.shape[0]:
         raise AssertionError("len(index) != len(labels)")