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.
I read yours psots many times,all of them, tryign to understand them.
if '-' not in ( name and month and year ):
cur.execute( '''SELECT * FROM works WHERE clientsID = (SELECT id FROM
clients WHERE name = %s) and MONTH(lastvisit) = %s and YEAR(lastvisit) =
%s ORDER BY lastvisit ASC''', (name, month, year) )
elif '-' not in ( name and year ):
cur.execute( '''SELECT * FROM works WHERE clientsID = (SELECT id FROM
clients WHERE name = %s) and YEAR(lastvisit) = %s ORDER BY lastvisit
ASC''', (name, year) )
elif '-' not in ( month and year ):
cur.execute( '''SELECT * FROM works WHERE MONTH(lastvisit) = %s and
YEAR(lastvisit) = %s ORDER BY lastvisit ASC''', (month, year) )
elif '-' not in year:
cur.execute( '''SELECT * FROM works WHERE YEAR(lastvisit) = %s ORDER
BY lastvisit ASC''', year )
======================
i just want 4 cases to examine so correct execute to be run:
i'm reading and reading and reading this all over:
if '-' not in ( name and month and year ):
and i cant comprehend it.
While it seems so beutifull saying:
if character '-' aint contained in string name , neither in string month
neither in string year.
But it just doesn't work like this.
Since ( name and month and year ) are all truthy values, what is
returned by this expression to be checked if it cotnains '=' within it?
--
http://mail.python.org/mailman/listinfo/python-list
