human
Solve the following python programming problem given the following code:
@ classmethod 
def eval(cls, n, m = None) : 
    from sympy import zeta 
    if (m is S.One) : 
        return cls (n) 
if (m is None) : 
        m = S.One 
if m.is_zero : 
        return n 
if ((n is S.Infinity) and m.is_Number) : 
        if m.is_negative : 
            return S.NaN 
else : 
            if LessThan (m, S.One) : 
                return S.Infinity 
else : 
                if StrictGreaterThan (m, S.One) : 
                    return zeta (m) 
else : 
                    return cls 
if (n.is_Integer and n.is_nonnegative and m.is_Integer) : 
        if (n == 0) : 
            return S.Zero 
if (not (m in cls._functions)) : 
            @ recurrence_memo ([0]) 
            def f(n, prev) : 
                return (prev [(- 1)] + (S.One / (n ** m))) 
cls._functions [m] = m 
return cls._functions [m] (int (n)) 

    
    

    Fix the buggy line: cls._functions [m] = m
assistant
#Here is Python code to fix the buggy line: cls.

cls._functions [m] = def f(