_win32sysloader now uses the same LoadLibrary flags as Python itself (f…

…ixes #1787) (#1794)

CHANGES.txt

@@ -8,6 +8,9 @@ Note that build 228 was the last version supporting Python 2.
 
 Since build 302:
 ----------------
+* Tweaks to how DLLs are loaded and our installation found, which should
+  improve virtualenv support and version mismatch issues (#1787, #1794)
+
 * Binary installers for 32-bit 3.10+ are no longer released (#1805)
 
 Since build 301:

win32/Lib/pywintypes.py

@@ -79,20 +79,32 @@ def __import_pywin32_system_module__(modname, globs):
             # easy_install...
             if os.path.isfile(os.path.join(os.path.dirname(__file__), filename)):
                 found = os.path.join(os.path.dirname(__file__), filename)
+
+        # There are 2 site-packages directories - one "global" and one "user".
+        # We could be in either, or both (but with different versions!). Factors include
+        # virtualenvs, post-install script being run or not, `setup.py install` flags, etc.
+
+        # In a worst-case, it means, say 'python -c "import win32api"'
+        # will not work but 'python -c "import pywintypes, win32api"' will,
+        # but it's better than nothing.
+        # We prefer the "user" site-packages if it exists...
+        if found is None:
+            import site
+
+            maybe = os.path.join(site.USER_SITE, "pywin32_system32", filename)
+            if os.path.isfile(maybe):
+                found = maybe
+
+        # Or the "global" site-packages.
         if found is None:
-            # We might have been installed via PIP and without the post-install
-            # script having been run, so they might be in the
-            # lib/site-packages/pywin32_system32 directory.
-            # This isn't ideal as it means, say 'python -c "import win32api"'
-            # will not work but 'python -c "import pywintypes, win32api"' will,
-            # but it's better than nothing...
             import sysconfig
 
             maybe = os.path.join(
                 sysconfig.get_paths()["platlib"], "pywin32_system32", filename
             )
             if os.path.isfile(maybe):
                 found = maybe
+
         if found is None:
             # give up in disgust.
             raise ImportError("No system module '%s' (%s)" % (modname, filename))

win32/src/_win32sysloader.cpp

@@ -56,8 +56,17 @@ static PyObject *PyLoadModule(PyObject *self, PyObject *args)
     TCHAR *modName = NULL;
     if (!PyArg_ParseTuple(args, fmt, &modName))
         return NULL;
-    HINSTANCE hinst = LoadLibrary(modName);
 
+    // Python 3.7 vs 3.8 use different flags for LoadLibraryEx and we match them.
+    // See github issue 1787.
+#if (PY_VERSION_HEX < 0x03080000)
+    HINSTANCE hinst = LoadLibraryEx(modName, NULL,
+                                    LOAD_WITH_ALTERED_SEARCH_PATH);
+#else
+    HINSTANCE hinst = LoadLibraryEx(modName, NULL,
+                                    LOAD_LIBRARY_SEARCH_DEFAULT_DIRS |
+                                    LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
+#endif
     if (hinst == NULL) {
         Py_INCREF(Py_None);
         return Py_None;