From f06536d4ac1ea0ddf00c1255fc37316ded089caf Mon Sep 17 00:00:00 2001
From: Kenneth Hsu <kennethshsu@gmail.com>
Date: Thu, 4 Jun 2026 15:59:40 -0700
Subject: [PATCH 1/2] Added development_format

---
 chainladder/utils/data/_manifest.py    |  4 ++++
 chainladder/utils/utility_functions.py | 17 +++++++----------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/chainladder/utils/data/_manifest.py b/chainladder/utils/data/_manifest.py
index bf21d808..75702d6a 100644
--- a/chainladder/utils/data/_manifest.py
+++ b/chainladder/utils/data/_manifest.py
@@ -27,6 +27,8 @@
     Measure column name(s) loaded into the Triangle.
 ``cumulative``
     ``True`` if the measures are cumulative, ``False`` if incremental.
+``development_format``
+    Optional. Passed to ``Triangle`` by :func:`chainladder.load_sample`.
 """
 
 SAMPLES: dict = {
@@ -157,6 +159,7 @@
             "Paid Claims",
         ],
         "cumulative": True,
+        "development_format": "%Y-12-31",
     },
     "friedland_med_mal": {
         "origin": "Accident Year",
@@ -169,6 +172,7 @@
             "Open Claim Counts",
         ],
         "cumulative": True,
+        "development_format": "%Y",
     },
     "friedland_qs": {
         "origin": "Accident Year",
diff --git a/chainladder/utils/utility_functions.py b/chainladder/utils/utility_functions.py
index 7e8ac606..11335cb8 100644
--- a/chainladder/utils/utility_functions.py
+++ b/chainladder/utils/utility_functions.py
@@ -10,10 +10,7 @@
 import numpy as np
 import pandas as pd
 
-from chainladder import (
-    __dt64_unit__,
-    __dt64_dtype__
-)
+from chainladder import __dt64_unit__, __dt64_dtype__
 from chainladder.utils.sparse import sp
 from chainladder.utils.data._manifest import SAMPLES
 from io import StringIO
@@ -117,6 +114,8 @@ def load_sample(key: str, *args, **kwargs) -> Triangle:
     columns = config["columns"]
     cumulative = config["cumulative"]
 
+    development_format = config.get("development_format", None)
+
     df = pd.read_csv(filepath_or_buffer=dataset_path)
 
     return Triangle(
@@ -126,6 +125,7 @@ def load_sample(key: str, *args, **kwargs) -> Triangle:
         index=index,
         columns=columns,
         cumulative=cumulative,
+        development_format=development_format,
         *args,
         **kwargs,
     )
@@ -818,6 +818,7 @@ def PTF_formula(
         return "+".join(formula_parts)
     return ""
 
+
 def date_delta_adjustment(date: str) -> str:
     """
     Subtracts the default pandas datetime delta from a date in "YYYY-MM-DD" string format.
@@ -855,10 +856,6 @@ def date_delta_adjustment(date: str) -> str:
         '2025-10-31 23:59:59.999999'
     """
 
+    res: str = str(pd.Timestamp(date) - pd.Timedelta(1, unit=__dt64_unit__))
 
-    res: str = str(
-        pd.Timestamp(date) - \
-        pd.Timedelta(1, unit=__dt64_unit__)
-    )
-
-    return res
\ No newline at end of file
+    return res

From 3993b4a8f3459780d2986b51281d953329b87ab0 Mon Sep 17 00:00:00 2001
From: Kenneth Hsu <kennethshsu@gmail.com>
Date: Thu, 4 Jun 2026 16:04:00 -0700
Subject: [PATCH 2/2] removed the development_format from friedland_med_mal

---
 chainladder/utils/data/_manifest.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/chainladder/utils/data/_manifest.py b/chainladder/utils/data/_manifest.py
index 75702d6a..21589a8e 100644
--- a/chainladder/utils/data/_manifest.py
+++ b/chainladder/utils/data/_manifest.py
@@ -172,7 +172,6 @@
             "Open Claim Counts",
         ],
         "cumulative": True,
-        "development_format": "%Y",
     },
     "friedland_qs": {
         "origin": "Accident Year",