reading file/dll which is already present to system environment path

Question

I am adding some folder path to system environment and need to open that file using ctypes

I get error: File not found (or something similar). I ran in debug mode and tested os.path.isfile(<file_name_without_full_path>) but got False

when I run os.getenv("path") I get folder path of that file. eg: C:\some_folder\folder_containing_DLL available in path