[Tutor] using 'and ' and 'or' with integers

[Mitya Sirenef]

On Wed 09 Jan 2013 01:56:20 AM EST, ken brockman wrote:
> I was looking through some lab material from a computer course offered
> at UC Berkeley and came across some examples in the form of questions
> on a test about python.
> 1 and 2 and 3
>  answer 3
> I've goggled it till i was red in the fingers, but to no avail.. Could
> someone be kind enuff to direct me to some docs that explain this??
> I've no clue what the hell is going on here..
> Thanks much for any help you may supply.
>
>
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It returns last evaluated value. If you have '1 and 2', 1
is 'truthy', so it needs to evaluate 2, and then 2 is returned.

With '0 and 2', 0 is falsy, so it does not need to evaluate
past it and returns 0.

With '0 or 2', it needs to evaluate 2 and returns its value.

This is particularly useful to assign only when a value is
falsy:

default_x = 5

def f(x):
  x = x or default_x


So if x is provided, it is used, but if x is, let's say, None,
default_x will be used.


HTH,  - mitya




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Lark's Tongue Guide to Python: http://lightbird.net/larks/