Given a dictionary of data and this widget's name, returns the value
        of this widget. Returns None if it's not provided.

def value_from_datadict(self, data, files, name):
        """
        Given a dictionary of data and this widget's name, returns the value
        of this widget. Returns None if it's not provided.
        """
        value = super(FileSizeWidget, self).value_from_datadict(data, files, name)
        if value not in EMPTY_VALUES:
            try:
                return parse_size(value)
            except ValueError:
                pass
        return value