[Tutor] Help with Guess the number script

[eryksun]

On Sat, Mar 8, 2014 at 1:44 PM, Scott dunning <swdunning at cox.net> wrote:
>> if 1 > guess > 100:
>>
> OH!  I see what you're saying, ignore my last post.  Yes that looks
> cleaner.

Please read section 6.9 of the language reference, which defines
Python comparison expressions.

http://docs.python.org/3/reference/expressions#not-in

Here's the description of chained comparisons:

    Comparisons can be chained arbitrarily, e.g.,
    x < y <= z is equivalent to x < y and y <= z,
    except that y is evaluated only once (but in
    both cases z is not evaluated at all when
    x < y is found to be false).

    Formally, if a, b, c, ..., y, z are expressions
    and op1, op2, ..., opN are comparison operators,
    then a op1 b op2 c ... y opN z is equivalent to
    a op1 b and b op2 c and ... y opN z, except
    that each expression is evaluated at most once.

    Note that a op1 b op2 c doesn’t imply any kind
    of comparison between a and c, so that, e.g.,
    x < y > z is perfectly legal (though perhaps
    not pretty).

Thus `1 > guess > 100` is equivalent to `(guess < 1) and (guess >
100)`, which is always false. The correct chained comparison is `not
(1 <= guess <= 100)`.

Chaining is generally simpler, since all expressions are only
evaluated once. In this particular case, with a local variable
compared to constants, the chained form is slightly less efficient in
CPython. Though if it "looks cleaner" to you, certainly use it.
Readability takes precedence.