python程序为什么不接受任何输入

我的代码是:

print("welcome into my program")
print("you want to know the percentage then type yes")
o=input
if str(o)=='yes':
    t=input("enter the total marks\n")
    x=input("enter your marks\n")
    p=(int(x)*100)/int(t)
    print("This is your percentage =",p)
else:
    print("bye :)")

输出:

welcome into my program
you want to know the percentage then type yes
bye :)

I search on it but I did not find any thing. When I try to run my program it just ignores my input line and goes ahead to print from the else block.