Python：为什么“ [1,2,3]中的2 == True”返回False？

Question

Suppose I enter this in Shell, then I get True .

>>>ar=[2,4,6,8]
>>>2 in ar
True

But when I try to use this, it doesn't work

>>>if 2 in ar==True:
       print("YES")

>>> 
>>> 

It doesn't work! The if condition is False. What can I do to check whether a term is there in a list with a loop? For example: I am given some random list and I have to print all the even numbers present in the list?

Answer 1

That is because with comparison operators, x operator1 y operator2 z is equivalent to (x operator1 y) and (y operator2 z) except that y is evaluated only once. Therefore 2 in ar == True is equivalent to (2 in ar) and (ar == True) . ar == True is False, so the if block is not executed. Just put parentheses around 2 in ar : if (2 in ar) == True: You really don't need the == True , though. Just do if 2 in ar: .