x = r"\mathjax{{color}}{{text}}"

result = r"\mathjax{{color}}{{text}}".format(color = "blue" , text = "Spanish")

result = "\mathjax{blue}{Spanish}"   

Can we change str.format so that it is possible to change only one string parameter, but leave the other parameters alone?

# pfr is partially_formatted_result 
pfr    = r"\mathjax{{color}}{{text}}".format(color = "blue")   # ERROR! missing parameter `text`
result = r"\mathjax{{color}}{{text}}".format(text = "Spanish") # ERROR! missing parameter `color`
The implementation requires fewer than ten lines of code in python, probably less than fifty lines in C, or a different implementation language.   
class str:
    def format(self, **kwargs):
        for key in kwargs:  
            x = "{"+key+"}"
            ostr   = kwargs[key].join(self.split(x))  
        return ostr # output string    

As an example, everywhere a string contained `{text}` it will now say `Spanish` .