On Wednesday, April 6, 2011 6:06:06 AM UTC-4, Νικόλαος Κούρας wrote:
>
> The trouble was in `if "@" in mail` .
> You can only test somthing `in` something else if the second thing is
> iterable and None isnt.
>
> So i made the code look like this:
>
> [code]
> if ( mail is not None and '@' in mail ) and comment not in ("Ρωτήστε
> με σχετικά...", "", None):
> [/code]
>
> Now it works like i wanted but i want to ask you if i wrote it
> correctly, especially when i check against `""` and None
You can also use an empty string as the default value when getting the field
value, which would simplify your test by eliminating None as a possibility. The
particulars will depend on your framework. For example, cgi.FieldStorage has a
getfirst method that takes a default value as the 2nd parameter.
Also, a simple OR statement can eliminate the None. For example: mail = mail or
''. Since None is False, the statement returns the right-hand operand, which is
an empty string ''.
> And please explain to me the difference betweeen an empty string `""`
> and None. An empty string is still a string with zero characters
> within?
Yes, an empty string is still of type 'str'. None is Python's null value of
type 'NoneType'. Its boolean value is False, and it does nothing special and
cannot be subclassed. When a function doesn't explicitly return a value, it
implicitly returns None.
> > Yes, I made a mistake. It should have been
> > `cursor.execute(SQL_COMMENT_FORM, (mail, comment))`, using a comma instead
> > of a '%' to have it generate SQL string literals from the tuple.
>
> What do you mean by "to have it generate SQL string literals from the
> tuple." Please explain
Here's an amusing warning from the Psycopg (PostgreSQL) docs:
"Warning: Never, never, NEVER use Python string concatenation (+) or string
parameters interpolation (%) to pass variables to a SQL query string. Not even
at gunpoint."
The line I wrote not only didn't properly quote or escape the data values, but
it probably also broke the protection from a SQL injection attack. Always list
the data in the 2nd parameter as a tuple.
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