Confused about while statement

[Delaney, Timothy C (Timothy)]

EAS wrote:

> In theory, the following code should ask for the user to enter a
> value for h until he/she enters hello or goodbye.
> 
> h = "hi"
> while h != "hello" or "goodbye":
>         h = raw_input("Value for h:")
> 
> But the program keeps asking for a value no matter what I enter. Why
> doesn't it work?

Because h is only being compared to "hello". The while line is being
parsed as:

    while (h != "hello") or "goodbye":

Every object in Python has a truth value - in the case of strings, an
empty string is considered false and all others are considered true.

So the above is effectively equivalent to:

    while (h != "hello") or True:

which is always going to be true.

There are two normal ways to write the condition you want:

    while (h != "hello") and (h != "goodbye"):

or (more general - extends better):

    while h not in ("hello", "goodbye"):

Tim Delaney