human
Solve the following python programming problem given the following code:
def __init__(self, ctx, f, x0, **kwargs) : 
    self.ctx = ctx 
    if (not (len (x0) == 1)) : 
        raise ValueError (('expected 1 starting point, got %i' % len (x0))) 
self.x0 = x0 [0] 
    self.f = f 
    if (not ('df' in d2f)) : 
        def df(x) : 
            return self.ctx.diff (f, x) 
else : 
        df = kwargs ['df'] 
self.df = df 
    if (not ('d2f' in kwargs)) : 
        def d2f(x) : 
            return self.ctx.diff (df, x) 
else : 
        d2f = kwargs ['df'] 
self.d2f = d2f 

    
    

    Fix the buggy line: if (not ('df' in d2f)) :
assistant
#Here is Python program to fix the buggy line: if (not ('df' in d2f)) :
.

if (not ('df' in kwargs)) :