From 6068a3cd43348d2f8d5881eb9b716e82f9a6c5b5 Mon Sep 17 00:00:00 2001
From: Rasaboun <40967731+Rasaboun@users.noreply.github.com>
Date: Fri, 7 Aug 2026 10:31:47 +0200
Subject: [PATCH] fix: name the config key when step scheduler is missing
 step_size

Without step_size, StepLR raises 'missing 1 required positional argument',
which is Python-level phrasing that does not tell a config author the value
belongs under lr_scheduler_params. Raise with the config path instead.

Deliberately an error rather than a default: step_size determines the shape
of the entire lr curve, so a guessed value would train to completion and
quietly produce a worse result with no signal anything was wrong.
---
 toolkit/scheduler.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/toolkit/scheduler.py b/toolkit/scheduler.py
index 2404ae69..ab87f68b 100644
--- a/toolkit/scheduler.py
+++ b/toolkit/scheduler.py
@@ -24,6 +24,11 @@ def get_lr_scheduler(
         # StepLR decays purely on step_size/gamma and has no notion of run
         # length, so drop the total_iters the trainer injects.
         kwargs.pop('total_iters', None)
+        if 'step_size' not in kwargs:
+            raise ValueError(
+                "lr_scheduler 'step' requires lr_scheduler_params.step_size "
+                "(number of steps between each lr decay)"
+            )
 
         return torch.optim.lr_scheduler.StepLR(
             optimizer, **kwargs