From 8788edb20a51c03541bcbbe2c77f186d0c2d78ee Mon Sep 17 00:00:00 2001
From: tatianag <tatianag@ipac.caltech.edu>
Date: Thu, 5 Dec 2024 17:09:44 -0800
Subject: [PATCH] DM-47976: Support conversion field in file template format
 strings

---
 doc/changes/DM-47976.bugfix.md                     | 1 +
 python/lsst/daf/butler/datastore/file_templates.py | 6 +++++-
 tests/test_templates.py                            | 9 +++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 doc/changes/DM-47976.bugfix.md

diff --git a/doc/changes/DM-47976.bugfix.md b/doc/changes/DM-47976.bugfix.md
new file mode 100644
index 0000000000..1c427373a8
--- /dev/null
+++ b/doc/changes/DM-47976.bugfix.md
@@ -0,0 +1 @@
+Support type conversion field in file template format strings.
diff --git a/python/lsst/daf/butler/datastore/file_templates.py b/python/lsst/daf/butler/datastore/file_templates.py
index 85cbc8d93a..5496bdf952 100644
--- a/python/lsst/daf/butler/datastore/file_templates.py
+++ b/python/lsst/daf/butler/datastore/file_templates.py
@@ -571,7 +571,7 @@ def format(self, ref: DatasetRef) -> str:
         parts = fmt.parse(self.template)
         output = ""
 
-        for literal, field_name, format_spec, _ in parts:
+        for literal, field_name, format_spec, conversion in parts:
             if field_name and "|" in field_name:
                 alternates = field_name.split("|")
                 for alt in alternates:
@@ -678,6 +678,10 @@ def format(self, ref: DatasetRef) -> str:
                 if replace_slash:
                     value = value.replace("/", "_")
 
+            # Apply conversion (e.g., integer to string)
+            if conversion:
+                value = fmt.convert_field(value, conversion)
+
             # Now use standard formatting
             output = output + literal + format(value, format_spec)
 
diff --git a/tests/test_templates.py b/tests/test_templates.py
index 9f66ba5e49..0d288861ad 100644
--- a/tests/test_templates.py
+++ b/tests/test_templates.py
@@ -152,6 +152,15 @@ def testBasic(self):
             self.makeDatasetRef("calexp", run="run.2", dataId=dataId),
         )
 
+        # Check that type conversion is applied
+        dataId = {"instrument": "dummy", "day_obs": 20250203}
+        tmplstr = "{run}/{datasetType}/{day_obs!s:.4s}"
+        self.assertTemplate(
+            tmplstr,
+            "run3/calexp/2025",
+            self.makeDatasetRef("calexp", run="run3", dataId=dataId),
+        )
+
         with self.assertRaises(FileTemplateValidationError):
             FileTemplate("no fields at all")