Add condition for a virtual environment on Windows to contain a Pytho…

…n executable

fawltydeps/types.py

@@ -148,18 +148,20 @@ class PyEnvSource(Source):
     def __post_init__(self) -> None:
         super().__post_init__()
         assert self.path.is_dir()  # sanity check
-        # Support vitualenvs, poetry2nix envs, system-wide installs, etc.
-        if self.path.match("lib/python?.*/site-packages"):
-            if (self.path.parent.parent.parent / "bin/python").is_file():
-                return  # all ok
-        # Also support projects using __pypackages__ from PEP582:
-        elif self.path.match("__pypackages__/?.*/lib"):
-            return  # also ok
 
         # Support Windows projects
-        if sys.platform.startswith("win") and self.path.match(
-            os.path.join("Lib", "site-packages")
-        ):
+        if sys.platform.startswith("win"):
+            if self.path.match(str(Path("Lib", "site-packages"))):
+                if (self.path.parent.parent / "Scripts" / "python.exe").is_file():
+                    return  # also ok
+        # Support vitualenvs, poetry2nix envs, system-wide installs, etc.
+        else:
+            if self.path.match("lib/python?.*/site-packages"):
+                if (self.path.parent.parent.parent / "bin/python").is_file():
+                    return  # all ok
+
+        # Also support projects using __pypackages__ from PEP582:
+        if self.path.match("__pypackages__/?.*/lib"):
             return  # also ok
 
         raise ValueError(f"{self.path} is not a valid dir for Python packages!")