From 45bb2b9a52a866772d4524904b95306dc899a6cd Mon Sep 17 00:00:00 2001
From: Yufeng He <40085740+he-yufeng@users.noreply.github.com>
Date: Thu, 18 Jun 2026 15:07:25 +0800
Subject: [PATCH] fix(utils): strip the _qlib_ prefix in fname_to_code, not
 characters

fname_to_code used fname.lstrip("_qlib_") to undo code_to_fname's prefix, but
str.lstrip removes any leading characters that appear in its argument, not the
prefix as a whole. exists_qlib_data() lowercases the feature directory name
before calling fname_to_code, so a reserved device code such as LPT1 (stored as
"_qlib_LPT1") becomes "_qlib_lpt1" and then "pt1" instead of "lpt1" -- the
leading "l" is wrongly stripped because it is one of the prefix characters.
Remove the prefix by slicing so the original code is recovered intact.
---
 qlib/utils/__init__.py   |  5 ++++-
 tests/misc/test_utils.py | 17 +++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/qlib/utils/__init__.py b/qlib/utils/__init__.py
index 2a94ebd555b..0f4d7b10876 100644
--- a/qlib/utils/__init__.py
+++ b/qlib/utils/__init__.py
@@ -932,7 +932,10 @@ def fname_to_code(fname: str):
 
     prefix = "_qlib_"
     if fname.startswith(prefix):
-        fname = fname.lstrip(prefix)
+        # NOTE: use slicing rather than ``lstrip(prefix)``; ``str.lstrip`` strips
+        # any leading characters contained in ``prefix`` (e.g. it would turn
+        # "_qlib_lpt1" into "pt1"), not the prefix as a whole.
+        fname = fname[len(prefix) :]
     return fname
 
 
diff --git a/tests/misc/test_utils.py b/tests/misc/test_utils.py
index db5b0724886..0b0a01c2573 100644
--- a/tests/misc/test_utils.py
+++ b/tests/misc/test_utils.py
@@ -10,6 +10,7 @@
 from qlib.constant import REG_CN, REG_US, REG_TW
 from qlib.utils.time import cal_sam_minute as cal_sam_minute_new, get_min_cal, CN_TIME, US_TIME, TW_TIME
 from qlib.utils.data import guess_horizon
+from qlib.utils import code_to_fname, fname_to_code
 
 REG_MAP = {REG_CN: CN_TIME, REG_US: US_TIME, REG_TW: TW_TIME}
 
@@ -127,6 +128,22 @@ def test_guess_horizon(self):
         result = guess_horizon(label)
         assert result == 5
 
+
+class FileNameUtils(TestCase):
+    def test_fname_code_round_trip(self):
+        # code_to_fname only prefixes reserved Windows device names; fname_to_code
+        # must strip the whole "_qlib_" prefix, not individual characters.
+        # exists_qlib_data() lowercases the directory name before converting back,
+        # and "lpt*" begins with characters that are also in the prefix.
+        for code in ["CON", "PRN", "AUX", "NUL", "COM1", "LPT1", "LPT9"]:
+            fname = code_to_fname(code)
+            self.assertEqual(fname_to_code(fname.lower()), code.lower())
+
+        # a name whose body consists only of prefix characters must survive
+        self.assertEqual(fname_to_code("_qlib_lll"), "lll")
+        # plain codes pass through unchanged
+        self.assertEqual(fname_to_code("AAPL"), "AAPL")
+
         label = ["Ref($close, -1) / Ref($close, -1) - 1"]
         result = guess_horizon(label)
         assert result == 1