How to check if string input is a number? [duplica

Question

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• How can I check if a string represents an int, without using try/except? 14 answers

How do I check if a user's string input is a number (e.g. -1, 0, 1, etc.)?

user_input = input("Enter something:")

if type(user_input) == int:
    print("Is a number")
else:
    print("Not a number")

The above won't work since input always returns a string.

Answer 1

For Python 3 the following will work.

userInput = 0
while True:
  try:
     userInput = int(input("Enter something: "))       
  except ValueError:
     print("Not an integer!")
     continue
  else:
     print("Yes an integer!")
     break 

Answer 2

Simply try converting it to an int and then bailing out if it doesn't work.

try:
   val = int(userInput)
except ValueError:
   print("That's not an int!")

Answer 3

while True:
    b1=input('Type a number:')
    try:
        a1=int(b1)
    except ValueError:
        print ('"%(a1)s" is not a number. Try again.' %{'a1':b1})       
    else:
        print ('You typed "{}".'.format(a1))
        break

This makes a loop to check whether input is an integer or not, result would look like below:

>>> %Run 1.1.py
Type a number:d
"d" is not a number. Try again.
Type a number:
>>> %Run 1.1.py
Type a number:4
You typed 4.
>>> 

Answer 4

try this! it worked for me even if I input negative numbers.

  def length(s):
    return len(s)

   s = input("Enter the String: ")
    try:
        if (type(int(s)))==int :
            print("You input an integer")

    except ValueError:      
        print("it is a string with length " + str(length(s)))   

Answer 5

a=10

isinstance(a,int)  #True

b='abc'

isinstance(b,int)  #False

Answer 6

I also ran into problems this morning with users being able to enter non-integer responses to my specific request for an integer.

This was the solution that ended up working well for me to force an answer I wanted:

player_number = 0
while player_number != 1 and player_number !=2:
    player_number = raw_input("Are you Player 1 or 2? ")
    try:
        player_number = int(player_number)
    except ValueError:
        print "Please enter '1' or '2'..."

I would get exceptions before even reaching the try: statement when I used

player_number = int(raw_input("Are you Player 1 or 2? ") 

and the user entered "J" or any other non-integer character. It worked out best to take it as raw input, check to see if that raw input could be converted to an integer, and then convert it afterward.