Python data structure for dice roll emulator

Question

So I made a dice rolling simulator in python, and while it does everything that I want it to I was told I could implement lists or a dictionary and it would be "better" code. I have tried adding both to my code and am completely lost. If any of you could help/show me that would be awesome. Here's my code, thanks so much.

from random import randint
print ""
die_amount = raw_input(">How many dice would you like to roll?: " )
die_amount = int(die_amount)
print ""
print "\t %s die are being rolled:" % die_amount
def dieroll(die_amount):
 one = 0
 two = 0
 three = 0
 four = 0
 five = 0
 six = 0
 for i in range(1, die_amount+1):
 roll = randint(1,6)
 print "\t You rolled: %s" % roll
 if roll == 1:
 one +=1
 elif roll == 2:
 two +=1
 elif roll ==3:
 three +=1
 elif roll == 4:
 four +=1
 elif roll == 5:
 five+=1
 elif roll == 6:
 six +=1
 print """ 
 One's rolled: %s
 Two's rolled: %s
 Three's rolled: %s
 Four's rolled: %s
 Five's rolled: %s
 Six's rolled: %s
 """ % (one, two, three, four, five, six )
 return [one, two, three, four, five, six]
dieroll(die_amount)

• boardrider: Regarding '"better" code' @rcline6: you may wan't to execute python -c "import this" from the shell to read The Zen of Python.

Answer 1

A Counter data structure does exactly what you are trying to do.

from collections import Counter
c = Counter()
for i in range(die_amount):
 roll = randint(1,6)
 c[roll] += 1

Or, even easier:

c = Counter(randint(1,6) for i in range(die_amount))

c[1] then contains the number of times 1 was rolled etc.

To print out the roll counts, you can use

for number, count in c.iteritems():
 print "{}'s rolled: {}".format(number, count)

---

A Counter is basically a Python dictionary with a default value of zero. This makes it particularly suitable for counting how many objects occur in a list, for instance.

There are several reasons why this approach works better than keeping a separate variable for each count.

• If you wanted to have a hundred-sided dice, you would have to define 100 separate variables. That's much more error prone.

• It's, in principle, much faster. Having six different variables necessitates looping through them with a series of if-statements. Imagine you roll a six. You will have to evaluate five different if-statements until you get to if roll == 6. By contrast, the counter uses a hash table, so c[roll] takes the same amount of time, regardless of how many rolls you make.

This begs the question: how can you know when you should be using a collection as opposed to a set of variables? The rule of thumb is that if a set of objects are different instances of the same thing, and we intend to use each object in exactly the same manner, they probably belong in a collection. In this case, a roll of 1 or a roll of 4 is essentially identical as far as the program flow is concerned. We will always treat them identically. They should therefore be kept in a collection.

• rcline6: Awesome! this sounds like it is exactly what I needed. Now where would I put it in my code? Can I just add the second code to my for loop? how would I get it to print out? Thanks so much!
• Pascal Bugnion: You probably want the import statement at the top. The body of your die_roll function should then just become return Counter(randint(1,6) for i in range(die_amount)). I suggest moving the print statements to a separate function (that way, you can re-use your die roll function in different programs without cluttering up your output).
• Pascal Bugnion: I suggest you take some of the bits that I outlined and play with them in a Python shell to get an idea of how they fit together.
• rcline6: Okay you are awesome, I got it to work so at the end it would print it in this format ({6:3, 3:1, 4:1}) like that if I rolled 5 dice, would I be able to print a counter in order like 1:0, 2:0 3:1 ect. or could I not? also could I add a string to it like in my code or no? But thank you, it was a huge help!
• Pascal Bugnion: The print statement wrapped in a for-loop in my answer should print 1's rolled: 0 ... Is that not what you want -- you may want to read about Python's format statement (docs.python.org/2/library/stdtypes.html#str.format )? In general, you can iterate through elements in a dictionary (or a counter) with a for loop like for key, value in c.iteritems(): #do something with key and value . You should be able to modify this to print however you like.

Answer 2

If you want an answer that more closely matches your original implementation, but uses a list instead, here is a replacement for dieroll():

def dieroll(die_amount):
 rolls = [0] * 6
 for i in range(die_amount):
 roll = randint(1,6)
 print "\t You rolled: %s" % roll
 rolls[roll-1] += 1
 print """ 
 One's rolled: %s
 Two's rolled: %s
 Three's rolled: %s
 Four's rolled: %s
 Five's rolled: %s
 Six's rolled: %s
 """ % tuple(rolls)
 return rolls

• rcline6: This is awesome! that allows me to still print my strings! Thanks for the help!