Why is the code (Python) giving error?

Question

import numpy as np
import matplotlib.pyplot as plt
class Prisoners_Dilemma:
 def __init__(self,n,p):
 self.n = n
 self.p = p
 def decision_array(self):
 self.dict_dict = {}
 for i in range(1,self.n + 1):
 self.dict_dict[i] = []
 list_list = []
 for j in range(1,self.n): 
 #np.random.seed(j)
 self.r = np.random.uniform(0,1)
 if self.r > self.p:
 q = 0
 else:
 q = 1
 list_list.append(q) 
 self.dict_dict[i] = list_list
 return self.dict_dict
 def payoff(self):
 self.dict_dict_2 = {}
 for i in range(1,self.n + 1):
 self.dict_dict_2[i] = []
 list_list_2 = []
 list_list_3=[]
 for j in range(1, i):
 list_list_2.append(self.dict_dict[j][i-2])
 for j in range(i + 1, self.n + 1):
 list_list_2.append(self.dict_dict[j][i-1])
 list_list_2_np = np.array(list_list_2)
 against_i = np.sum(list_list_2_np)
 for_i = np.sum(self.dict_dict[i]) 
 if against_i == 0 and for_i == 0:
 payoff_i = 2
 elif against_i == 0 and for_i != 0:
 payoff_i = 5
 elif against_i != 0 and for_i == 0:
 payoff_i = -5
 else:
 payoff_i = -2
 list_list_3.append(payoff_i)
 self.dict_dict_2[i]=list_list_3
 return self.dict_dict_2
 def gameplay(self, N, initial_count):
 self.counter = initial_count
 for i in range(N):
 for j in range(1, self.n + 1):
 z = self.dict_dict_2[j]
 x = np.array(z)
 self.counter += np.sum(z)
 return self.counter
y = Prisoners_Dilemma(15,0.015)
print (y.gameplay(20,100))

In the above code, the compiler gives the error that instance has no attribute as dict_dict_2 even though its prefixed with self. Moreover, it is perfectly fine with dict_dict. For the sake of completeness I have included the whole code but the problem lies only in payoff and gameplay methods?

Answer 1

dict_dict_2 is only created in payoff(), therefore you must call it before attempting to call gameplay().

• Manish Kumar Singh: could you then explain why dict_dict variable works (see payoff and decision_matrix) ?
• Ignacio Vazquez-Abrams: It "works" by accident, because you never access it.

Answer 2

The issue is that you are only creating self.dict_dict_2 variable in the payoff function, but in your logic where you are calling gameplay() function , you are not calling the payoff() function before accessing dict_dict_2 , from the looks of it you are not calling that function anywhere at all.

Not sure what dict_dict_2 holds, but the above is the reason why you are getting the issue, maybe you can move the initialization part of dict_dict_2 to __init__() function , though that would not fix the complete issue, since you would still be trying to access dict_dict_1[j] which can error out if j is not a key in dict_dict_2 .

• Manish Kumar Singh: could you then explain why no such problem with dict_dict variable??
• Anand S Kumar: You are not accessing dict_dict variable anywhere in gameplay at all, you try accessing that there (just do simple print(self.dict_dict)) and you will see the error for that as well
• Manish Kumar Singh: not in the gameplay. I invoked dict_dict in decision_matrix and used it in payoff without any special syntax, still it works fine and gives me the list (if you try running the code by commenting the gameplay part).
• Anand S Kumar: You are defining dict_dict in the starting of decision_matrix , the line for the definition is - self.dict_dict = {} , this defines the variable dict_dict inside self .