fix: correct release date

news/date.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* Fix missing `__date__`, use PyPI release date.
+
+**Security:**
+
+* <news item>

src/diffpy/pdffit2/version.py

@@ -14,15 +14,46 @@
 ##############################################################################
 """Definition of __version__."""
 
-#  We do not use the other three variables, but can be added back if needed.
-__all__ = ["__date__", "__git_commit__", "__timestamp__", "__version__"]
-
-# obtain version information
+import datetime
+import json
+import urllib.request
 from importlib.metadata import version
+from pathlib import Path
+
+
+def get_pypi_release_date(package_name, timeout=5):
+    package_file = Path(__file__).resolve()
+
+    try:
+        with open(package_file, "r", encoding="utf-8") as f:
+            lines = f.readlines()
+        for line in reversed(lines):
+            if line.startswith("# Release date:"):
+                return line.split(":", 1)[1].strip()
+
+        url = f"https://pypi.org/pypi/{package_name}/json"
+        with urllib.request.urlopen(url, timeout=timeout) as response:
+            data = json.loads(response.read().decode("utf-8"))
+
+        installed_version = version(package_name)
+        release_data = data["releases"].get(installed_version, [])
+        if not release_data:
+            raise ValueError(f"No release data found for version {installed_version}")
+
+        release_date_str = release_data[-1]["upload_time"]
+        release_date = datetime.datetime.fromisoformat(release_date_str).date()
+
+        with open(package_file, "a", encoding="utf-8") as f:
+            f.write(f"\n# Release date: {release_date}")
+
+    except (ValueError, OSError) as e:
+        print(f"Warning: Could not fetch release date from PyPI: {e}")
+        release_date = datetime.datetime.fromtimestamp(package_file.stat().st_ctime).isoformat()
+
+    return str(release_date)
+
 
 __version__ = version("diffpy.pdffit2")
-__date__ = __all__[0]
-__git_commit__ = __all__[1]
-__timestamp__ = __all__[2]
+__date__ = get_pypi_release_date("diffpy.pdffit2")
 
 # End of file