PartialFormatter

Python partial string formatter

from string import Formatter

class PartialFormatter(Formatter):
    def format(self, format_string, *args, **kwargs):
        self.fields = kwargs.keys()

    def parse(self, format_string):
        for parsed in super(PartialFormatter, self).parse(format_string):
            if parsed[1] and parsed[1] not in self.fields:
                literal_text = parsed[0] + "{" + parsed[1]
                if parsed[2] is not None and len(parsed[2]) > 0:
                    literal_text += ":" + parsed[2]
                if parsed[3] is not None and len(parsed[3]) > 0:
                    literal_text += "!" + parsed[3]
                literal_text += "}" 
                yield (literal_text, None, None, None)
            else:
                yield parsed