A certainl part of an if() structure never gets executed.

[Νικόλαος Κούρας]

On 13/6/2013 4:55 πμ, Steven D'Aprano wrote:
> On Wed, 12 Jun 2013 14:17:32 +0300, Νικόλαος Κούρας wrote:
>
>> doesn't that mean?
>>
>> 		if '=' not in ( name and month and year ):
>>
>> if '=' does not exists as a char inside the name and month and year
>> variables?
>>
>> i think it does, but why it fails then?
>
> No. Python is very close to "English-like", but not exactly, and this is
> one of the easiest places to trip.
>
> In English:
>
> "the cat is in the box or the cupboard or the kitchen"
>
> means:
>
> "the cat is in the box, or the cat is in the cupboard, or the cat is in
> the kitchen".
>
>
> But that is not how Python works. In Python, you have to say:
>
> cat in box or cat in cupboard or cat in kitchen
>
>
> Although this will work as well:
>
> any(cat in place for place in (box, cupboard, kitchen))
>
>
> In Python, an expression like this:
>
> cat in (box or cupboard or kitchen)
>
>
> has a completely different meaning. First, the expression in the round
> brackets is evaluated:
>
> (box or cupboard or kitchen)
>
>
> and then the test is performed:
>
> cat in (result of the above)
>
>
> The expression (box or cupboard or kitchen) means "return the first one
> of box, cupboard, kitchen that is a truthy value, otherwise the last
> value". Truthy values are those which are considered to be "like True":
>
> truthy values:
>
> - True
> - object()
> - numbers apart from zero
> - non-empty strings
> - non-empty lists
> - non-empty sets
> - non-empty dicts
> - etc.
>
> falsey:
>
> - False
> - None
> - zero (0, 0.0, Decimal(0), Fraction(0), etc.)
> - empty string
> - empty list
> - empty set
> - empty dict
> - etc.
>
> (Can you see the pattern?)
>
>
> So you can experiment with this yourself:
>
> 42 or 23 or "foo"
> => the first object is truthy, so it is returned
>
> 0 or 23 or "foo"
> => the first object is falsey, and the second object is truthy,
> so it is returned
>
> 0 or [] or "foo"
> => the first two objects are falsey, so the third is returned
>
>
> The "and" operator works in a similar fashion. Experiment with it and see
> how it works for yourself.

First i wan tot thank you for taking the time to explain to me (the 
languages examples to explai encode-decode was really great as well)


So, baring in ming your explanation:

if '=' not in ( name or month or year )

first eval the expr. The expr will result to return the first object 
that has a truthy values.

in this particular example all 3 strings are truthies because they all 
contain characters inside them, the one user submitted when hitting the 
submit button

so that would turn to if '=' not in ( name ).
Allright, but what i wanted to check is if the char '=' ain't contained 
in both 3 strings not for the 1st string(name) which will always be true.

So i guess having it like this "if '=' not in ( name or month or year )" 
  is wrong?


b) Also what "if '=' not in ( name and month and year )" returns in the 
round brackets since in my case all the strings have values therefore 
they are true, which string get returned?