Python: IndexError: list index out of range

Question

I think I have my program completed, but... it doesn't work. I'm trying to write a program that simulates a lottery game, but when I try to check the user's guesses against the number of guesses on the ticket, I get an error that tells me the "list index is out of range". I think it has something to do with the part of the code where I assign the random digits to "a," "b", "c", etc. But I'm not sure.

Here is the code in it's entirety:

import random

def main():
random.seed()

#Prompts the user to enter the number of tickets they wish to play.
tickets = int(input("How many lottery tickets do you want?\n"))

#Creates the dictionaries "winning_numbers" and "guess." Also creates the variable "winnings" for total amount of money won.
winning_numbers = []
guess = []
winnings = 0

#Generates the winning lotto numbers.
for i in range(tickets):
    del winning_numbers[:]

    a = random.randint(1,30)
    while not (a in winning_numbers):
        winning_numbers.append(a)

    b = random.randint(1,30)
    while not (b in winning_numbers):
        winning_numbers.append(b)

    c = random.randint(1,30)
    while not (c in winning_numbers):
        winning_numbers.append(c)

    d = random.randint(1,30)
    while not (d in winning_numbers):
        winning_numbers.append(d)

    e = random.randint(1,30)
    while not (e in winning_numbers):
        winning_numbers.append(e)

    print(winning_numbers)
    getguess(guess, tickets)
    nummatches = checkmatch(winning_numbers, guess)

    print("Ticket #"+str(i+1)+": The winning combination was",winning_numbers,".You matched",nummatches,"number(s).\n")

    if nummatches == 0 or nummatches == 1:
        winnings = winnings + 0
    elif nummatches == 2:
        winnings = winnings + 10
    elif nummatches == 3:
        winnings = winnings + 500
    elif nummatches == 4:
        winnings = winnings + 20000
    elif nummatches == 5:
        winnings = winnings + 1000000

print("You won a total of",winnings,"with",tickets,"tickets.\n")

#Gets the guess from the user.
def getguess(guess, tickets):
del guess[:]

for i in range(tickets):
    bubble = input("What numbers do you want to choose for ticket #"+str(i+1)+"?\n").split(" ")
    guess.append(bubble)
print(bubble)

#Checks the user's guesses with the winning numbers.
def checkmatch(winning_numbers, guess):
match = 0
for i in range(5):

    if guess[i] == winning_numbers[i]:
        match = match+1

return match

main()

And here is the error I get:

Traceback (most recent call last):
  File "C:\Users\Ryan\Downloads\Program # 2\Program # 2\lottery.py", line 85, in <module>
    main()
  File "C:\Users\Ryan\Downloads\Program # 2\Program # 2\lottery.py", line 45, in main
   nummatches = checkmatch(winning_numbers, guess)
File "C:\Users\Ryan\Downloads\Program # 2\Program # 2\lottery.py", line 79, in checkmatch
    if guess[i] == winning_numbers[i]:
IndexError: list index out of range

Solution 1

As the error notes, the problem is in the line:

if guess[i] == winning_numbers[i]

The error is that your list indices are out of range--that is, you are trying to refer to some index that doesn't even exist. Without debugging your code fully, I would check the line where you are adding guesses based on input:

for i in range(tickets):
    bubble = input("What numbers do you want to choose for ticket #"+str(i+1)+"?\n").split(" ")
    guess.append(bubble)
print(bubble)

The size of how many guesses you are giving your user is based on

# Prompts the user to enter the number of tickets they wish to play.
tickets = int(input("How many lottery tickets do you want?\n"))

So if the number of tickets they want is less than 5, then your code here

for i in range(5):

if guess[i] == winning_numbers[i]:
    match = match+1

return match

will throw an error because there simply aren't that many elements in the guess list.

Solution 2

Here is your code. I'm assuming you're using python 3 based on the your use of print() and input():

import random

def main():
    #random.seed() --> don't need random.seed()

    #Prompts the user to enter the number of tickets they wish to play.

    #python 3 version:
    tickets = int(input("How many lottery tickets do you want?\n"))

    #Creates the dictionaries "winning_numbers" and "guess." Also creates the variable "winnings" for total amount of money won.
    winning_numbers = []
    winnings = 0

    #Generates the winning lotto numbers.
    for i in range(tickets * 5):
        #del winning_numbers[:] what is this line for?
        randNum = random.randint(1,30)
        while randNum in winning_numbers:    
            randNum = random.randint(1,30)
        winning_numbers.append(randNum)

    print(winning_numbers)
    guess = getguess(tickets)
    nummatches = checkmatch(winning_numbers, guess)

    print("Ticket #"+str(i+1)+": The winning combination was",winning_numbers,".You matched",nummatches,"number(s).\n")

    winningRanks = [0, 0, 10, 500, 20000, 1000000]

    winnings = sum(winningRanks[:nummatches + 1])

    print("You won a total of",winnings,"with",tickets,"tickets.\n")


#Gets the guess from the user.
def getguess(tickets):
    guess = []
    for i in range(tickets):
        bubble = [int(i) for i in input("What numbers do you want to choose for ticket #"+str(i+1)+"?\n").split()]
        guess.extend(bubble)
        print(bubble)
    return guess

#Checks the user's guesses with the winning numbers.
def checkmatch(winning_numbers, guess):
    match = 0
    for i in range(5):
        if guess[i] == winning_numbers[i]:
            match += 1
    return match

main()

Solution 3

I think you mean to put the rolling of the random a,b,c, etc within the loop:

a = None # initialise
while not (a in winning_numbers):
    # keep rolling an a until you get one not in winning_numbers
    a = random.randint(1,30)
    winning_numbers.append(a)

Otherwise, a will be generated just once, and if it is in winning_numbers already, it won't be added. Since the generation of a is outside the while (in your code), if a is already in winning_numbers then too bad, it won't be re-rolled, and you'll have one less winning number.

That could be what causes your error in if guess[i] == winning_numbers[i]. (Your winning_numbers isn't always of length 5).

Comments

[Joel Cornett]

This will code will only run if a is NOT in winning_numbers. In other words, if there is a repeat, no number will be appended. Remember, while checks the run condition before running.

[Joel Cornett]

Actually, his errors are being caused a little earlier down the line. Based on his input statement, bubble is a list of strings. This list then gets appended to guess. So guess would look something like: [['12', '30', '12', '23'. '3'], ['4','5','7','8','16']]. The proper list method is guess.extend(). Also, the values are strings, so even when they do compare, the comparison will never return true.