One of the things that has made Python successful is its readability. Code is clear and easy to understand. One of the reasons is that Python uses words for a few things that other languages use symbols for. But sometimes the readability is misleading. Beginners construct valid Python expressions that don’t do what they seem like they should do.

Let’s say you want to know if your variable x is equal to 17. You could do:

if x is 17:

This might work. But then if you try:

if name is "Ned":

it doesn’t work? What!? Why not? It’s so clear.

The problem is that “is” doesn’t check two values for equality, it checks if the left and right side are precisely the same object. But you can have two different string objects, each of which has the value “Ned”. You don’t use “is” to check equality, you use “==”:

if name == "Ned":

It’s not just strings: numbers can also do surprising things:

>>> 1000 + 1 is 1001
False

“x is 17” is more English-like than “x == 17”, but it isn’t right. This is one time that Python’s famed readability leads you to the wrong construct.

Another example: you need to know if the answer was either “y” or “yes”, so you try this:

if answer == "y" or "yes":
    print("Thanks")

and now your program doesn’t work. No matter what answer is, it prints “Thanks.” Why?

The “or” operator is for combining boolean (true/false) expressions. The result is true if either of its operands is true. So your code is equivalent to:

if (answer == "y") or ("yes"):
    print("Thanks")

If answer is “y”, then the if will be true. If answer isn’t “y”, then the or will consider the right-hand side, “yes”. Strings are true if they are not empty, so “yes” is always true. So the if condition will always be true, no matter what value answer has.

The right ways to do this are:

if answer == "y" or answer == "yes":
    print("Thanks")

or if you want to be fancier,

if answer in {"y", "yes"}:
    print("Thanks")

(a list or a tuple would also work here instead of a set, though then you get into philosophical debates about how many data structures fit on the head of a pin.)

Don’t get me wrong, I agree that Python is very readable. And every language has constructs that seem like they should work, but don’t. You have to study well, and be careful to use your chosen language properly.