# /usr/bin/env python3
# -*- coding: utf-8 -*-
import math
def quadratic(a, b, c):
	if not isinstance(a+b+c, (int, float)):
		raise TypeError('bad operand type')
	d=b*b-4*a*c
	if a==0:
		return'a can not be zero'
	elif d<0:
		return'no result'
	elif d==0:
		x1=x2=-b/(2*a)
		return('%.1f %.1f' % (x1, x2))
	elif d>0:
	    x1=(-b+ math.sqrt(d))/(2*a)
	    x2=(-b- math.sqrt(d))/(2*a)
	    return('%.1f %.1f' % (x1, x2))
a=float(input('a='))
b=float(input('b='))
c=float(input('c='))
print(quadratic(a,b,c))
#test
print('quadratic(2,3,1)=', quadratic(2,3,1))
print('quadratic(1,3,-4)=', quadratic(1,3,-4))
if quadratic(2,3,1) != (-0.5, -1.0):
	print('failure')
elif quadratic(1,3,-4) != (1.0,-4.0):
	print('failure')
else:
	print('successful')

输入a=1,b=3,c=-4，输出结果也是（1.0，-4.0），为什么测试结果是失败的，求各位大佬帮看看，谢谢！