pity.py

class g:
    def __init__(self):
        self.s = "f"
    def __call__(self, c=None):
        if c is None:
            self.s += "o"
            return self
        else:
            return self.s+c
def f(c=None):
    return g()(c)

print f('l')
print f()('l')
print f()()()()('l')