file.py 文件源码

def __call__(self, form, field):
        if not (isinstance(field.data, FileStorage) and field.data):
            return

        filename = field.data.filename.lower()

        if isinstance(self.upload_set, Iterable):
            if any(filename.endswith('.' + x) for x in self.upload_set):
                return

            raise StopValidation(self.message or field.gettext(
                'File does not have an approved extension: {extensions}'
            ).format(extensions=', '.join(self.upload_set)))

        if not self.upload_set.file_allowed(field.data, filename):
            raise StopValidation(self.message or field.gettext(
                'File does not have an approved extension.'
            ))