'Define the conversion from item value to displayed text.
If a string is specified, it is used as a format string for converting
float values (and all other types are converted using str). If a
function is specified, it will be called with the item as its only
argument and must return a string.
Added in version 0.9.9.'

def setFormat(self, fmt):

    if ((fmt is not None) and (not isinstance(fmt, basestring)) and (not callable(fmt))):
        raise ValueError(('Format    argument    must    string,    callable,    or    None.    (got    %s)' % fmt))
    self._format = fmt
    self._updateText()
