How to not include character or string input in the array (Python)

Question

I'm trying to write a simple program where a variable will store the input type in by a user until the word "done" is seen. After that, the program will print out the maximum and minimum value store in the variable. However, I would like to prevent the variable from storing characters or strings where the user may accidentally type in. What are ways that I can use? Try and except?

a=0
store1=''
store2=''
while store1 !='done':
     store1 = input('Enter a number: ')
     store2=store2+' '+store1
     a =a+1
store3=store2.split()
store4=store3[:a-1]
print('Maximum: %s'%(max(store4)))
print('Minimum: %s'%(min(store4)))

I tried another way and I got this problem. Does anyone know what is wrong?

def RepresentsInt(s):
    try: 
        int(s)
        return True
    except ValueError:
        return False
a=0
store1=''
store2=''
while store1 !='done':
    store1 = input('Enter a number: ')
    b = RepresentsInt(store1)
    if(b==True): 
        store2=store2+' '+store1
    #        a =a+1
 store3=store2.split()
 #store4=store3[:a-1]
 print(store3)
 print('Maximum: %s'%(max(store3)))
 print('Minimum: %s'%(min(store3)))
 #print(len(store3))

The stored value seems to contain only numbers in string-format. However, when it prints out the max and min values, it doesn't print out the correct max and min as the picture shown below.

Answer 1

Using your current implementation (number of issues), here's how you'd perform the check:

a=0
store1=''
store2=''
while store1 !='done':
  store1 = input('Enter a number: ')
  if store1 == 'done':
    break;
  try:
    int(store1)
  except ValueError:
    continue
  store2=store2+' '+store1
  a =a+1
store3=store2.split()
store4=store3[:a-1]
print('Maximum: %s'%(max(store4)))
print('Minimum: %s'%(min(store4)))

I added in an immediate check for the input value (otherwise it executes the with the 'done' value, causing the Maximum: d output).

For the input checking, the approach is trying to convert the string to an integer and returning to the start of the loop if a ValueError is caught.

Using this looks like:

$ python3 input.py
Enter a number: 1
Enter a number: 2
Enter a number: what
Ivalid input.
Enter a number: 3
Enter a number: 4
Enter a number: done
Maximum: 3
Minimum: 1

So, we still have a problem with actually finding the maximum value. Which begs the question, why all the string manipulation?

Here's a simpler implementation using an array instead:

numbers = []
while True:
  input_value = input('Enter a number: ')
  if input_value == 'done':
    break
  try:
    int_value = int(input_value)
  except ValueError:
    print("Ivalid input.")
    continue
  numbers.append(int_value)

print('Maximum: %s'%(max(numbers)))
print('Minimum: %s'%(min(numbers)))

Usage:

$ python3 input.py
Enter a number: 1
Enter a number: 2
Enter a number: what
Ivalid input.
Enter a number: 3
Enter a number: 4
Enter a number: done
Maximum: 4
Minimum: 1

---

EDIT: The problem with your second attempt is that you are performing a lexicographic sort, instead of a numerical one. This is due to fact that the array is storing string values.

# sorting strings, lexicographically
>>> [x for x in sorted(['1000', '80', '10'])]
['10', '1000', '80']

# sorting numbers, numerically
>>> [x for x in sorted([1000, 80, 10])]
[10, 80, 1000]

In my fixed example above, the strings are converted to integer values before they get stored in the array, so they end up being sorted numerically.