The EINVAL error in Windows also needs improvement, but I don't what can be done after the fact. If there's a trailing slash when opening or creating a regular file, the NtCreateFile system call returns STATUS_OBJECT_INVALID_NAME. The Windows API maps this to ERROR_INVALID_NAME (123), which the CRT in turn maps to EINVAL (22). This error is too generic to handle. Even if the name ends in a slash, the error could be due to some other invalid character in the path (e.g. a common mistake is a '\t' or '\n' in a string literal). 

The problem could be addressed beforehand in shutil.copy by manually raising an exception if isdir() is false and the name has a trailing slash.