import math

def quadratic_equation(a, b, c):

    y = b*b - 4*a*c

    if y < 0:

        return 

    else:

        x1 = (-b+math.sqr(y))/(2*a)

        x2 = (-b-math.sqr(y))/(2*a)

        return x1,x2

print quadratic_equation(2, 3, 0)

print quadratic_equation(1, -6, 5)

cmd显示如下：

F:\PythonTest>python test.py

Traceback (most recent call last):

  File "test.py", line 12, in <module>

    print quadratic_equation(2,3,0)

  File "test.py", line 9, in quadratic_equation

    x1 = (-b+math.sqr(y))/(2*a)

AttributeError: 'module' object has no attribute 'sqr'