Add Windows DLL loading fix for Python 3.8+

Co-authored-by: sbillinge <4254545+sbillinge@users.noreply.github.com>

Author: Copilot

src/diffpy/srreal/__init__.py

@@ -14,6 +14,20 @@
 ##############################################################################
 """Tools for real space structure analysis."""
 
+# Windows DLL loading fix for Python 3.8+
+# On Windows, add the conda library bin directory to DLL search path
+# before importing extension modules that depend on DLLs
+import os
+import sys
+
+if sys.platform == "win32" and sys.version_info >= (3, 8):
+    # Try to add conda library bin directory to DLL search path
+    conda_prefix = os.environ.get("CONDA_PREFIX")
+    if conda_prefix:
+        lib_bin_dir = os.path.join(conda_prefix, "Library", "bin")
+        if os.path.isdir(lib_bin_dir):
+            os.add_dll_directory(lib_bin_dir)
+
 # package version
 from diffpy.srreal.version import __version__
 

tests/test_dll_loading.py

@@ -0,0 +1,33 @@
+"""Unit tests for Windows DLL loading initialization."""
+
+import os
+import sys
+
+
+def test_import_succeeds():
+    """Ensure diffpy.srreal can be imported successfully on all platforms."""
+    import diffpy.srreal
+
+    assert hasattr(diffpy.srreal, "__version__")
+
+
+def test_windows_dll_directory_handling():
+    """Verify Windows DLL directory handling doesn't raise errors."""
+    # This test verifies that the Windows-specific DLL directory initialization
+    # in __init__.py doesn't cause issues on any platform.
+    
+    # The actual DLL directory logic is executed during module import,
+    # so if we got this far, it succeeded.
+    
+    # On Windows with Python 3.8+, verify the logic would have run
+    if sys.platform == "win32" and sys.version_info >= (3, 8):
+        # Check that CONDA_PREFIX environment variable handling works
+        conda_prefix = os.environ.get("CONDA_PREFIX")
+        if conda_prefix:
+            lib_bin_dir = os.path.join(conda_prefix, "Library", "bin")
+            # The directory should exist in a proper conda environment
+            # but we don't assert this as it may not exist in all test environments
+            assert isinstance(lib_bin_dir, str)
+    
+    # Test passes if no exceptions are raised
+    assert True