How to run a method on an argument in a formatted string

[Exsul]

class Test:

    def __init__(self):
        self.name = "unnamed"
        self.subj = "he"
        self.poss = "his"
        self.obj = "him"
        self.reflex = "himself"

    def quirks(self):
        return "{0.subj} is happy.".format(self)


test_NPC1 = Test()

print(test_NPC1.quirks())

Output:
he is happy.

Process finished with exit code 0

I want to be able to run a method, like .capitalize(), on the string value passed into the placeholder in the formatted text above, but I'm not sure how to do it. If I place it after .format(self), it affects the entire string, which is not what I want. I want to apply it specifically to the string value that is passed in.

[Exsul]

The answer was f-strings. return f"{self.subj.capitalize()} is happy."