Probability Calculator - 2 stupid questions I'm stuck on

[lucasbalestrassi]

Hey guys, I’m stuck on 2 issues.

1 - When I run the experiment, i get an error on test #1 which according to the test_module.py should return expected = [“red”,“red”,“red”,“blue”,“blue”], which is exactly what my code returns. However the test indicated that it should return:

• [‘green’,
• ‘green’,
• ‘blue’,
• ‘blue’,
• ‘green’,
• ‘green’,
• ‘blue’,
• ‘green’,
• ‘blue’,
• ‘green’,
• ‘red’,
• ‘red’,
• ‘red’,
• ‘red’,
• ‘red’,
• ‘blue’,
• ‘blue’]

2 - I keep getting None as a result for my sort method, which I am using to compare the strings. I’ve looked everywhere and I can’t figure out what is going on.

    if drawn.sort() == expected.sort(): 
        M +=1

Below is my replit code

import copy
import random
# Consider using the modules imported above.

class Hat:

    contents = []
    drawn = []
    
    def __init__(self,**data):
        v = 0
        for key,value in data.items():
            while v < value:
                self.contents.append(key)
                v+=1
            v=0
        # print(contents)
    
    def __str__(self):
        a = str(self.contents)
        return a
        
    def draw(self,number):
        if number <= len(self.contents):
            for n in range(number):
                n = random.randint(0,len(self.contents)-1)
                self.drawn.append(self.contents.pop(n))
                # print(len(self.contents))
            return self.drawn
        else:
            for n in range(len(self.drawn)):
                self.contents.append(self.drawn.pop(0))
            return self.drawn

def experiment(hat, expected_balls, num_balls_drawn, num_experiments):
    
    prob = 0
    # print("hat is ",hat)
    M = 0
    
    
    expected = []
    v=0
    for key,value in expected_balls.items():
        while v < value:
            expected.append(key)
            v+=1
        v=0
    
    for n in range(num_experiments):
        drawn = []
        myhat = hat
        drawn = myhat.draw(num_balls_drawn)

        
        if drawn.sort() == expected.sort():
            M +=1
        #print(M)
        
        
        #essa linha zera drawn e myhat
        myhat.draw(len(hat.contents)+1)
        
    
    prob = M / num_experiments
    
    return prob

Link to the challenge:

freeCodeCamp.org

[jeremy.a.gray]

@lucasbalestrassi

class Hat:

    contents = []
    drawn = []

These are class variables and not instance variables as they are declared here. So all objects of that class are using the same bit of memory (and values) for those variables.

@lucasbalestrassi

2 - I keep getting None as a result for my sort method, which I am using to compare the strings.

Check the documentation. This is the documented behavior of the sort method on lists.

[lucasbalestrassi]

Jeremy,

Thanks for the answer. I was able to get through the questions but now i’m at the last bit: my probability is off by just a little bit.

I referred to this forum post that had the same issue but the hint you described there
still didn’t get me to realize what I am doing wrong. I am getting a 0.259 != 0.272 within 0.01 delta (0.013000000000000012 difference) : Expected experiment method to return a different probability.

Probability Calculator: Probability off by 0.01

Hey, I’ve been working on the python probability calculator, and it feels like I’m pretty close to completing it, however I’ve been getting a result for the experiments that has a probability of 0.262 which is 0.01 less than the expected result of 0.272 I’m wondering if anyone has any suggestions or advice as far as figuring out this last discrepancy as I’ve become quite stumped. Link to my replit: https://replit.com/@UnusualFrog/boilerplate-probability-calculator-5#prob_calculator.py Thanks! …

below is my code:

import copy
import random
# Consider using the modules imported above.

class Hat:

    contents = []
    drawn = []
    
    def __init__(self,**data):
        v = 0
        
        self.contents.clear()
        self.drawn.clear()
        for key,value in data.items():
            while v < value:
                self.contents.append(key)   
                v+=1
            v=0
        # print(contents)
    
    def __str__(self):
        a = str(self.contents)
        return a
        
    def draw(self,number):
        if number <= len(self.contents):
            for n in range(number):
                n = random.randint(0,len(self.contents)-1)
                self.drawn.append(self.contents.pop(n))
                # print(len(self.contents))
            return self.drawn
        else:
            for n in range(len(self.drawn)):
                self.contents.append(self.drawn.pop(0))
            return self.drawn

def experiment(hat, expected_balls, num_balls_drawn, num_experiments):
    
    prob = 0
    # print("hat is ",hat)
    M = 0
    
    
    expected = []
    
    v=0
    for key,value in expected_balls.items():
        while v < value:
            expected.append(key)
            v+=1
        v=0
    
    for n in range(num_experiments):
        drawn = []
        myhat = hat
        drawn = myhat.draw(num_balls_drawn)

        sdrawn = sorted(drawn)
        # print(sdrawn)
        sexpected = []
        sexpected = sorted(expected)
        # print(sexpected)

        # print(M)
        for s in expected:
            if s in sdrawn:
                sdrawn.remove(s)
                sexpected.remove(s)
                # print(sdrawn)
                # sdrawn.
            if sexpected == []:
                M+=1
                
        #essa linha zera drawn e myhat
        myhat.draw(len(hat.contents)+1)
        
    
    prob = M / (num_experiments)
    
    return prob

Not sure if this deserves a new post

[JeremyLT]

@lucasbalestrassi

   contents = []
    drawn = []

I would just delete these lines instead of messing around with clearing the contents. Using class variables like this can lead to very confusing results.

[lucasbalestrassi]

Hey Jeremy, if I delete these lines I get an error that the Hat class doesn`t have contents as an attribute.

Is this related to my probability being a little off or is it just code optimization?

Thanks

[JeremyLT]

You delete those lines and then you need to fix your initialization to accommodate that change.

[lucasbalestrassi]

Hello,

My probability is a little off. From what I have read, previous users have had troubles calculating the probability.

I get the following error:
AssertionError: 0.259 != 0.272 within 0.01 delta (0.013000000000000012 difference) : Expected experiment method to return a different probability.

I’ve tried troubleshooting my code but I can’t figure out which situation I am calculating the probability wrong.

import copy
import random
# Consider using the modules imported above.

class Hat:

    
    def __init__(self,**data):
        v = 0

        self.contents=[]
        self.drawn=[]
        for key,value in data.items():
            while v < value:
                self.contents.append(key)   
                v+=1
            v=0
        # print(contents)
    
    def __str__(self):
        a = str(self.contents)
        return a
        
    def draw(self,number):
        if number <= len(self.contents):
            for n in range(number):
                n = random.randint(0,len(self.contents)-1)
                self.drawn.append(self.contents.pop(n))
                # print(len(self.contents))
            return self.drawn
        else:
            for n in range(len(self.drawn)):
                self.contents.append(self.drawn.pop(0))
            return self.drawn
def experiment(hat, expected_balls, num_balls_drawn, num_experiments):
    prob = 0
    # print("hat is ",hat)
    M = 0 
    
    expected = []
    
    v=0
    for key,value in expected_balls.items():
        while v < value:
            expected.append(key)
            v+=1
        v=0
    
    for n in range(num_experiments):
        myhat = copy.copy(hat)
        drawn = myhat.draw(num_balls_drawn)

        sdrawn = copy.copy(drawn)
        # print(sdrawn)
        sexpected = copy.copy(expected)
        # print(sexpected)

        # print(M)
        for s in expected:
            if s in sdrawn:
                # print("drawn: ",sdrawn)
                # print("expected: ",sexpected)
                sdrawn.remove(s)
                sexpected.remove(s)
                # print(sdrawn)
                # sdrawn.
            else:
                break
            if sexpected == []:
                # print("success drawn: ",sdrawn)
                # print("success expected: ",sexpected)
                M+=1
                # print(M)
        #essa linha zera drawn e myhat
        myhat.draw(len(hat.contents)+1)
        
    
    prob = M / (num_experiments)
    

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Challenge: Scientific Computing with Python Projects - Probability Calculator

Link to the challenge:

freeCodeCamp.org

[JeremyLT]

@lucasbalestrassi

random.randint(0,len(self.contents)-1)

Is this method inclusive or exclusive of the upper bound?

Hmm, it’s inclusive.

I wouldn’t reuse the variable n there.

[JeremyLT]

@lucasbalestrassi

            for n in range(len(self.drawn)):
                self.contents.append(self.drawn.pop(0))
            return self.drawn

I’m not sure this is per the instructions. You shouldn’t need to put anything back. Just return all of the contents.

[lucasbalestrassi]

Hey @JeremyLT. Thanks for your comments, not sure I follow though

Since I am popping out of the original contents list (I didn’t create a copy), I need to make sure that the contents goes back to the original state after the draw. I added some coments to show what happens in the draw. (See below)

If it`s just the return bit your talking about, then yes I should change it to
return self.contents. Still can’t see how this is related to the probability

Original hat [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘red’, ‘green’, ‘green’, ‘green’, ‘green’, ‘green’, ‘green’]
contents = [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘red’, ‘green’, ‘green’, ‘green’, ‘green’, ‘green’] after 1 st draw
drawn = [‘green’] after 1 st draw
contents = [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘green’, ‘green’, ‘green’, ‘green’, ‘green’] after 2 st draw
drawn = [‘green’, ‘red’] after 2 st draw
contents = [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘green’, ‘green’, ‘green’, ‘green’] after 3 st draw
drawn = [‘green’, ‘red’, ‘green’] after 3 st draw
contents = [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘green’, ‘green’, ‘green’] after 4 st draw
drawn = [‘green’, ‘red’, ‘green’, ‘green’] after 4 st draw
Original hat [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘green’, ‘green’, ‘green’]
contents = [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘green’, ‘green’, ‘green’, ‘green’] after returning 1 ball
drawn = [‘red’, ‘green’, ‘green’] after returning 1 ball
contents = [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘green’, ‘green’, ‘green’, ‘green’, ‘red’] after returning 2 ball
drawn = [‘green’, ‘green’] after returning 2 ball
contents = [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘green’, ‘green’, ‘green’, ‘green’, ‘red’, ‘green’] after returning 3 ball
drawn = [‘green’] after returning 3 ball
contents = [‘blue’, ‘blue’, ‘blue’, ‘red’, ‘green’, ‘green’, ‘green’, ‘green’, ‘red’, ‘green’, ‘green’] after returning 4 ball
drawn = after returning 4 ball

[lucasbalestrassi]

I have altered the code:

        for n in range(number):
            r = random.randint(0,len(self.contents)-1)
            self.drawn.append(self.contents.pop(r))

[JeremyLT]

@lucasbalestrassi

I didn’t create a copy

You must create a copy. In order to prevent someone from just returning the theoretical probability, the number of experiments is somewhat low. But that means that the result is based upon repeated experiments with the balls back in their original order, which is disrupted if you ignore the advice to clone the hat.