Print the largest odd number entered

Question

I wrote this code to solve a problem from a John Vuttag book:

Ask the user to input 10 integers, and then print the largest odd number that was entered. If no odd number was entered, it should print a message to that effect.

Can my code be optimized or made more concise? Any tips or errors found?

{
 a = int (raw_input("enter num: "))
 b = int (raw_input("enter num: "))
 c = int (raw_input("enter num: "))
 d = int (raw_input("enter num: "))
 e = int (raw_input("enter num: "))
 f = int (raw_input("enter num: "))
 g = int (raw_input("enter num: "))
 h = int (raw_input("enter num: "))
 i = int (raw_input("enter num: "))
 j = int (raw_input("enter num: "))
 num_List = {a,b,c,d,e,f,g,h,i,j }
 mylist=[]
 ## Use for loop to search for odd numbers
 for i in num_List:
 if i&1 :
 mylist.insert(0,i)
 pass
 elif i&1 is not True: 
 continue
 if not mylist:
 print 'no odd integers were entered'
 else:
 print max (mylist)
}

• Johntron: Here's my response to a suspiciously similar question: codereview.stackexchange.com/questions/26187/…
• user25830: this question is a "finger exercise" in John Vuttag book, introduction to programming. Sorry if it was posted before
• Johntron: Oh no problem, I was just trying to help :)

Answer 1

Your main loop can just be:

for i in num_list:
 if i & 1:
 mylist.append(i)

There is no need for the else at all since you don't do anything if i is not odd.

Also, there is no need at all for two lists. Just one is enough:

NUM_ENTRIES = 10
for dummy in range(NUM_ENTRIES):
 i = int(raw_input("enter num: "))
 if i & 1:
 mylist.append(i)

Then the rest of the program is as you wrote it.

• user25830: Thanks! it looks cleaner. I am working on using one raw_input instead of 10
• fge: No problem! I am no Python specialist though
• tijko: @fge one small thing, wouldn't a for j in range(10) be better than incrementing in a while loop?
• fge: tijko: yup... I didn't know of range :p

Answer 2

This is a solution that doesn't use lists, and only goes through the input once.

maxOdd = None
for _ in range(10):
 num = int (raw_input("enter num: "))
 if num & 1:
 if maxOdd is None or maxOdd < num:
 maxOdd = num
if maxOdd:
 print "The max odd number is", maxOdd 
else:
 print "There were no odd numbers entered"

Answer 3

One other minor change you could make, would be to just loop over a range how many times you want to prompt the user for data:

mylist = list()
for _ in range(10):
 while True:
 try:
 i = int(raw_input("enter num: "))
 if i & 1:
 mylist.append(i)
 break
 except ValueError:
 print "Enter only numbers!"

No need to create an extra variable and increment it here.

• 200_success: Since you don't care about the value of j, it's customary to write for _ in range(10) instead.

Answer 4

My 2c: though I don't know Python syntax that well, here's an optimization idea that would be more important given a (much) bigger dataset.

You don't need any lists at all. On the outside of the loop, declare a "maximum odd" variable, initially equal to -1. On the inside of the loop, whenever a number is input, if it's odd and greater than maximumOdd, then set maximumOdd equal to that number. This requires nearly no memory, whereas building up a list and then operating on it scales linearly in memory (not good).

• user25830: I was trying to get the loop concept down, this is taking it to the next level, Thanks. Can you please tell me why you set the variable to -1
• Reinderien: The variable is set to -1, or some other value making it obvious that it's "unset". That way, if the loop runs through without finding any odd numbers, you can tell afterwards.

Answer 5

I'd write:

numbers = [int(raw_input("enter num: ")) for _ in range(10)]
odd_numbers = [n for n in numbers if n % 2 == 1]
message = (str(max(odd_numbers)) if odd_numbers else "no odd integers were entered")
print(message)