On Mon, 23 Feb 2009 21:56:46 -0700, Wes James wrote:
>> vars = {'_page': i}
>> if request.vars._query is not None:
>> vars['_query'] = request.vars._query
>
> Could this be:
>
> vars = {'_page': i}
> if request.vars._query:
> vars['_query'] = request.vars._query
Instead of typing "request.vars._query" in all the examples, I'm going to
abbreviate it as "x" instead.
"if x is not None" and "if x" are very different things. Consider the
following examples:
>>> x = None
>>>
>>> if x is not None:
... print "action performed when x is not None"
... else:
... print "do nothing"
...
do nothing
>>>
>>> if x:
... print "action performed when x is not None"
... else:
... print "do nothing"
...
do nothing
So far so good. Both pieces of code do the right thing when x actually is
None. But what happens if x is *not* None?
>>> x = "" # The empty string is *not* None.
>>>
>>> if x is not None:
... print "action performed when x is not None"
... else:
... print "do nothing"
...
action performed when x is not None
>>>
>>> if x:
... print "action performed when x is not None"
... else:
... print "do nothing"
...
do nothing
That's clearly wrong, because we know that x isn't None, it is the empty
string. The test "if x" does not test for the same thing as "if x is not
None". "if x" tests the general truth value of any object, and many
objects have a false truth value: None, empty string, 0, [], {} and many
more.
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
