I understand why this problem arose. If you parse an HTTP URL, its path always starts with "/" if not empty. And you usually want to interpret it as a relative to some base directory. But lstrip('/') works well here. In any case you need to have some validation to disallow "..".

I think that adding yet one operation will confuse users. And what to do with C:\foo\bar, C:foo\bar, \\?\c\foo\bar, etc?