Solution0 | Python Fiddle

from math import log, exp, pow

class Solution:

def __init__(self):
        """
            The constructor exists only to initialize variables. You do not need to change it.
        """
        self.evals=0
        self.tolerance=0.000001  #Set the tolerance for computing b
                
    def computeB(self,S,N):
        """ 
            Entry point for recursive computeB function
        """
        
        '''You need to set these to reasonable values'''
        upperBound= log(S,N)
        lowerBound= 1.000000
        
        lowerBound, upperBound = self.computeB_R(lowerBound,upperBound,S,N)
        
        return (lowerBound+upperBound)/2
        
    def computeB_R(self,lowerBound,upperBound,S,N):    
                        
        '''check stopping condition for recusion, stop on else'''
        if(upperBound-lowerBound) > self.tolerance:

'''compute mean'''
            guess=(upperBound+lowerBound)/2
            
           
            '''compute the expression using guess as b '''   
            val= 0.000000
            for x in range(1,N+1):
                val += pow(guess,x)
            
            '''figure out if guess was too high or too low'''
            if(val>=S):
                '''return a call to yourself with apprpriately changed bounds'''
                return self.computeB_R(lowerBound,guess,S,N)
            else:
                '''return a call to yourself with apprpriately changed bounds'''
                return self.computeB_R(guess,upperBound,S,N)
        else:
            return lowerBound,upperBound

if __name__ == "__main__" :

s=Solution()
     
     '''This is roughly what the grader does'''
     
     print("Testing 13 = b + b^2 + b^3 + b^4")
     ans=s.computeB(13,4)    
     if( (ans -  1.5326593400551733) < 0.000001):
            print("Yay, computeB(13,4) works!!")
     else:
         print("There seems to be something wrong with you script.")
         
     '''Testing Result - based on the euqatino this should add up to 13'''
    
     
     print("This should add up to 13: " , ans + ans**2 + ans**3 + ans**4)
         
     '''
     Note, since b is taken to large powers, the result can be sensitive.
     For large number computing b to 6 digital places might not be enough
     to get the exact value back.
     '''

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