python里对浮点数变量判断是否相等equal，不可以直接用==
a = 1.7
b = 0.9 + 0.8 # This should be 1.7
if a == b:
print("a and b are equal.")
else:
print("a and b are different !")
#返回结果是：a and b are different !
if abs(a-b) < 0.00001:
print("a and b are equal.")
else:
print("a and b are different !")
#返回结果：a and b are equal