为什么我这个一直输出的None,谢谢各位大佬了

Maximum_a = None
Minimum_a = None

while True:
inp = input("Enter a number: ")

if inp == "done":
    break

try:
    num_a = float(inp)
    print(num_a)
    if Minimum_a == None:
        num_a = Minimum_a
    elif num_a < Minimum_a:
        num_a = Minimum_a
    if Maximum_a == None:
        num_a = Maximum_a
    elif num_a > Maximum_a:
       num_a = Maximum_a
except:
    print ("Invalid input")

continue

print ("Maximum is", Maximum_a)
print ("Minimum is", Minimum_a)

仔细检查一下你会发现你一直在给他赋None值。所以不管你怎么输入都会被改成空值应该是把 num_a = Maximum_a 都改成 Maximum_a = num_a