How to output nothing

Question

Hi I wrote a program which tells me if there is or not hexadecimals in the input.

hexadecimal = ['0','1','2','3','4','5','6','7','8','9','a','A','b','B','c','C','d','D','e','E','f','F']
output = ''
for c in hexadecimal:
  digit = input('Digit: ')
  output += c.join(digit)
  if digit == '':
    print(output, 'is a valid hexadecimal string.')
    break
  elif digit not in hexadecimal:
    print(digit, 'is not a valid hexadecimal digit.')
    break

The complete code of this program works, the only problem is that I need to add this into my code when the user doesn't enter anything.

Possible duplicate of [Asking the user for input until they give a valid response](http://stackoverflow.com/questions/23294658/asking-the-user-for-input-until-they-give-a-valid-response) — dot.Py, Mar 15 '17 at 12:54
What on earth is this supposed to be doing? `for c in hexadecimal`...`c.join(digit)`. This is very confused code. — khelwood, Mar 15 '17 at 13:00
Are you just trying to write a script that takes input and tells you if its valid hex or not? — Hoopdady, Mar 15 '17 at 13:06

score 1 · Accepted Answer · answered Mar 15 '17 at 13:24

1

Use another if statement before appending it to output:

if len(output) == 0 and len(digit) == 0:
    print("input is blank")

This checks that the user hasn't previously entered anything and hasn't currently entered anything, if both are true then tell them the input is blank.

answered Mar 15 '17 at 13:24

Andria

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where would I put this in my code because I am not appending – cars Mar 15 '17 at 13:25
Before 'output +=' and after 'digit = input' – Andria Mar 15 '17 at 13:26
it says input is blank when nothing is entered but it also says is a valid hexidecimal string underneath it and I dont want it to say that – cars Mar 15 '17 at 13:28
add `break` after `print()` – Glrs Mar 15 '17 at 13:29
Put a continue statement – Andria Mar 15 '17 at 13:29

lyrjie · Answer 2 · 2017-03-15T13:02:51.563

0

Modify your if:

if digit == '':
  if len(output)==0:
    print('The input was blank')
    break
  else:
    print(output, 'is a valid hexadecimal string.')
    break
elif digit not in hexadecimal:
  print(digit, 'is not a valid hexadecimal digit.')
  break

edited Mar 15 '17 at 13:02

answered Mar 15 '17 at 13:00

lyrjie

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5

Maybe you should try this code yourself it doesnt work at all – cars Mar 15 '17 at 13:05
Of course I tried it before posting. Make sure your code is indented properly – lyrjie Mar 15 '17 at 13:06
try replacing that if statement you made with my code at the top it wont work – cars Mar 15 '17 at 13:06
@cars maybe you should try to do your homework by yourself, instead of talking in that manner? – Igor Mar 15 '17 at 14:09

Rafał Duraj · Answer 3 · 2017-03-15T13:34:18.030

0

Do it like this:

hexadecimal = ['0','1','2','3','4','5','6','7','8','9','a','A','b','B','c','C','d','D','e','E','f','F']
digit = input('Digit: ')

while digit is not '':
    if digit in hexadecimal:
        print(digit, 'is a valid hexadecimal string.')
    else:
        print(digit, 'is not a valid hexadecimal digit.')
    digit = input('Digit: ')

print('The input was blank')

It is better to use construction if digit in hexadecimal(it checks if provided input is in a given list) than doing for loop and inserting brakes.

edited Mar 15 '17 at 13:34

answered Mar 15 '17 at 13:25

Rafał Duraj

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2

its supposed too be a for loop – cars Mar 15 '17 at 13:29
It keeps asking the user until they enter without writing anything – cars Mar 15 '17 at 13:30
Sorry, I didn't get it. Surround it with simple while condition. – Rafał Duraj Mar 15 '17 at 13:33
can you edit your answer with the while loop. It is confusing in the comment – cars Mar 15 '17 at 13:33
Did it now. Hope it helps. – Rafał Duraj Mar 15 '17 at 13:34

score 0 · Answer 4 · answered Mar 15 '17 at 14:08

Another way to deal with this, could be to use the string module and the built in functions all() and any().
all() returns True if all elements of the input are true (or if the input is empty).
any() returns True if any element of the input is a hexadecimal value.

string.hexdigits value is: '0123456789abcdefABCDEF'

Code:

import string

digit = input('Digit: ')

if not digit:
    print('The input was blank.')

elif all(c in string.hexdigits for c in digit):
    print(digit, 'is a valid hexadecimal string.')

elif any(c in string.hexdigits for c in digit):
    print(digit, 'there are hexadecimals in digit')

else:
    print(digit, 'is not a hexadecimal string.')

How to output nothing

4 Answers4