How to check if string input is a number? [duplicate]

Answer 1

The method isnumeric() will do the job (Documentation for python3.x):

>>>a = '123'
>>>a.isnumeric()
True

But remember:

>>>a = '-1'
>>>a.isnumeric()
False

isnumeric() returns True if all characters in the string are numeric characters, and there is at least one character.

So negative numbers are not accepted.

Answer 2

This solution will accept only integers and nothing but integers.

def is_number(s):
    while s.isdigit() == False:
        s = raw_input("Enter only numbers: ")
    return int(s)


# Your program starts here    
user_input = is_number(raw_input("Enter a number: "))

Answer 3

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 4

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 5

Here is a simple function that checks input for INT and RANGE. Here, returns 'True' if input is integer between 1-100, 'False' otherwise

def validate(userInput):

    try:
        val = int(userInput)
        if val > 0 and val < 101:
            valid = True
        else:
            valid = False

    except Exception:
        valid = False

    return valid

Answer 6

Apparently this will not work for negative values, but it will for positive numbers.

Use isdigit()

if userinput.isdigit():
    #do stuff