correctDecimalString.py

def isInt(str):
    if len(str) < 1:
        return False
    if str[0] == '-':
        str = str[1:]
    dot = False
    for c in str:
        if c == '.' and dot == True:
            return False
        if c == '.' and len(str) > 1:
            dot = True
            continue
        if ('0' > c or c > '9'):
            return False
    return True