Bug in luigi.contrib.ftp.py on putting file to ftp from Windows

[TychonautVII]

When calling the "put" operation from a windows machine using luigi.contrib.ftp.RemoteFileSystem, the code fails with a max recursion depth error.

This seems to be due the call to normpath in the beginning of both the put methods

    def _sftp_put(self, local_path, path, atomic):
        normpath = os.path.normpath(path)
        directory = os.path.dirname(normpath)

From the OS docs https://docs.python.org/3/library/os.path.html, normath "On Windows, it converts forward slashes to backward slashes." Most FTP servers use forward slashes as separators, so this messes up the remote path.

I think adding somthing like

    def _sftp_put(self, local_path, path, atomic):
        normpath = os.path.normpath(path)
        directory = os.path.dirname(normpath)
        if os.path.sep =='\\':
            directory = directory.replace('\\','//')

might just be enough to fix it

I believe that this is a dupe of a ticket @elessarelfstone put in in the past that got closed due to inactivity. https://github.com/spotify/luigi/issues/2880

[TychonautVII]

A better improvement actually might be to just leave the remote name as is

[stale[bot]]

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[elessarelfstone]

so what's up? Can we add some fixes in next releases