, cls=None, mode='U')[source]

Attempt to guess the format of a file and return format str and kwargs.


fp : filepath or filehandle

The provided file to guess the format of. Filepaths are automatically closed; filehandles are the responsibility of the caller.

cls : type, optional

A provided class that restricts the search for the format. Only formats which have a registered reader or writer for the given cls will be tested. Default is None.


(str, kwargs)

A format name and kwargs for the corresponding reader.



This occurs when the format is not ‘claimed’ by any registered sniffer or when the format is ambiguous and has been ‘claimed’ by more than one sniffer.