Pathon：判断用户输入与0比较

import re
def is_zero(d):
    d = float(d)
    if d > 0:
        print ‘positive‘
    elif d < 0:
        print ‘negative‘
    else:
        print ‘zero‘
x = raw_input("Enter a number:")
while len(x)>0:
    if re.search(r"^(\-)?\d+(\.\d+)?$",x):
        is_zero(x)
        break
    else:
        print ‘please enter a number‘
        x = raw_input("Enter a numbe:")