If you run the installer without UI and without specifying an installation path, it will not install. For example: C:\> python-3.5.0rc4-amd64-webinstall.exe /passive The workaround is to specify TargetPath: C:\> python-3.5.0rc4-amd64-webinstall.exe /passive TargetPath="C:\Python35_x64" However, this workaround should not be necessary. We should use the default path based on the InstallAllUsers setting (false by default).
Adding Larry, as this either needs a fix or a prominent release note for 3.5.0 (or we document the bug in the docs). I *think* the fix will be fairly simple and constrained entire to one file. Should have something ready later today.