How to avoid empty input

Question

I'm very new to Python and I wrote this part of code where the user must choose between 3 values options. I'm able to check if user insert a value which is less then zero or higher then max but I'm not able to check if user insert no value.

user.choose_action()
choice = input("    Choose action:")
while int(choice) < 1 or int(choice) > 3:
    print("    " + "The choice must be between 1 and 3. Retry.")
    choice = input("    Choose action:")
index = int(choice) - 1
if index == 0:
    other things

This code throws while int(choice) < 1 or int(choice) > 3: ValueError: invalid literal for int() with base 10: ' ' and as far as I understood this error is thrown because I'm trying to convert an empty value to int. I tried to fix with different solutions, for example:

while int(choice) < 1 or int(choice) > 3 or choice == '' :
     rest of the code

or

try:
    choice = input("    Choose action:")
except SyntaxError:
    y = None

or

while int(choice) < 1 or int(choice) > 3 or choice is None :

but nothing seems to work! I know that probably this is very stupid to fix but I'm not able to understand why at moment! What am I doing wrong?

You cannot catch `SyntaxError`, if you are getting those, fix them — C.Nivs, May 14 '19 at 14:36
Possible duplicate of [Asking the user for input until they give a valid response](https://stackoverflow.com/questions/23294658/asking-the-user-for-input-until-they-give-a-valid-response) — quamrana, May 14 '19 at 14:42

score 3 · Accepted Answer · answered May 14 '19 at 14:40

Change the order of the condition:

while choice == '' or int(choice) < 1 or int(choice) > 3 :
     rest of the code

The difference is that due to short-circuiting, if the input is empty, then it won't try to evaluate the other conditions which would throw an error.

score 0 · Answer 2 · answered May 14 '19 at 14:39

0

You can use try-except block in this case.try something like this:

while():

   try:
      # your main code here
  except ValueError:
     print('please enter a value:)
     choice=input()

answered May 14 '19 at 14:39

Tojra

673
5
20

score 0 · Answer 3 · answered May 14 '19 at 14:47

0

Please use this

raw_input("Choose action:")

answered May 14 '19 at 14:47

Wang Liang

4,244
6
22
45

How to avoid empty input

3 Answers3