Using float()
def isfloat(num):
    try:
        float(num)
        return True
    except ValueError:
        return False
print(isfloat('s12'))
print(isfloat('1.123'))
Output
False True
Here, we have used try except in order to handle the ValueError if the string is not a float.
- In the function 
isfloat(), float() tries to convert num to float. If it is successful, then the function returnsTrue. - Else, 
ValueErroris raised and returnsFalse. 
For example, 's12' is alphanumeric, so it cannot be converted to float and False is returned; whereas, '1.123' is a numeric, so it is successfully converted to float.
Also Read: