these are the 2 python3 code,
{w for w in words if w[::-1] in words and len(w)==4}
{w for w in words if w==w[::-1]and len(w)==4}
In my point, w is the word in words, so w should equal with words，but the output is differently. Could someone help me, why the output is different?
if words is {'abba', 'abcd', 'dcba'} then the result of the first code will be {'abba', 'abcd', 'dcba'} while the second will return {'abba'}.
w==w[::-1] checks if the word is equal to its reverse while w[::-1] in words checks if the reverse of w is in words.
I guess those code sanples are doing really different things.
{w for w in words if w[::-1] in `words` and len(w)==4}
It includes element w from itterable words if only reversed w ("ABCD" => "DCBA") is also present at words and it's length is 4.
{w for w in words if w==w[::-1]and len(w)==4}
This includes element w from words if only w is equal to reversed w itself ("abba" = "abba") and it's length is 4