How to check for negative numbers at the beginning of a string?

Question

I am trying to add a piece of code to this string to check for a negative number in the first position. If the code identifies a negative number it should return "False". I'm having trouble with int and str at the user input command.

def is_number(S):
    #if s < 0:
        #print("False")
    #else:   
        try:
            float(s)
            return True
        except ValueError:
            pass
 
        try:
            import unicodedata
            unicodedata.numeric(s)
            return True
        except (TypeError, ValueError):
            pass
        return False
  
s = input()

is_number(s)

The above code should accept numeric and alpha inputs without throwing an error.

Answer 1

Is this what you want?

def check_negative(s):
    try:
        f = float(s)
        if (f < 0):
            return True
        # Otherwise return false
        return False
    except ValueError:
        return False

Not entirely sure if this is what you want though, maybe you should see ᴡʜᴀᴄᴋᴀᴍᴀᴅᴏᴏᴅʟᴇ3000's answer

Answer 2

You can replace your is_number function with this code:

def is_number(s):
    return str(s)[0] == '-' and len(str(s)) > 1

It is a function which checks whether the first character is a negative sign, and if it is, it will return true. Otherwise, the number cannot be negative, and it will then return false. However, if there is only a - sign, then it is neither and will return false. It only uses one line and is much simpler. It works for strings and floats too.