human
Solve the following python programming problem given the following code:
def add_fk(self, model, fk) : 
    for (m, fld) in self.fklist : 
        if (model is m) : 
            return 
self.fklist.append ((model, fk)) 
    def f(a, b) : 
        return cmp (((fmn (a [0]) + '.') + a [1].name), ((fmn (b [0]) + '.') + b [1].name)) 
from functools import cmp_to_key 
    self.fklist.sort (key = cmp_to_key (fld)) 

    
    

    Fix the buggy line: self.fklist.sort (key = cmp_to_key (fld))
assistant
#Here is Python program to fix the buggy line: self.

self.fklist.sort (key = cmp_to_key (def f())