It's not uncommon to encounter FTP servers which are misconfigured and return unroutable host IP (eg. internal IP) when using passive mode

See: https://superuser.com/a/1195591

Most FTP clients such as FileZilla and WinSCP use a workaround when they encounter such servers and connect to user's specified host instead.

> Command: PASV
> Answer: 227 Entering Passive Mode (10,250,250,25,219,237).
> Status:  Server sent passive reply with unroutable address. Using server address instead.

Currently Python's ftplib simply timeouts for these and doesn't work.

Please no. The mistake should be fixed in the misconfigured FTP server, not in ftplib, which should not make this event pass unnoticed or take arbitrary decisions. Filezilla is different than ftplib in that it's an end-user app. ftplib is not (e.g. it can be used for testing FTP server implementations, like pyftpdlib).

A possible alternative is making socket.create_connection() show the address in case of error, like we do in socket.create_server:
https://github.com/python/cpython/blob/8702b67dad62a9084f6c1823dce10653743667c8/Lib/socket.py#L803-L805
That would at least provide a hint on what's the real issue. If you want to provide a patch for that you have my blessing.

The problem is that most of time you have no control over that FTP server but you still want to download files from that FTP server using Python. Currently that's just not possible. Maybe there could be some flag to enable workarounds for these cases.

stage: patch review -> resolved