Modern Python Standard Library Cookbook

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Not all FTP servers support the same commands. The protocol saw many extensions over the years, so some commands might be missing or have a different semantic.

For example, the mlsd function might be missing, but you might have LIST or nlst, which can perform a similar job.

You can refer to RFC 959 to know how the FTP protocol should work, but frequently experimenting explicitly with the FTP server you should be connecting to is the best way to assess which commands and which signature it's going to accept.

Frequently, FTP servers implement a HELP command you can use it to fetch the list of supported functions.