why does this test not return False when testing an integer

Expect to get this to return False as the string contains an integer

def is_float(s):
    try:
        float(s)
        return True
    except ValueError:
        return False

list1 =[['a','4'],['20.1','4'],['100','4'],['102','10'],['31.3','10'],['c','10'],['113','12'],['s','12'],['32.9','12']]
print(is_float(list1[6][0]))

This returns true when the value is 113. I would expect a False as the number is an integer?