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Re: TypeError: iterable argument required

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  Re: TypeError: iterable argument required "eryksun ()" <eryksun@gmail.com> - 2011-04-06 06:54 -0700
    Re: TypeError: iterable argument required Νικόλαος Κούρας <nikos.kouras@gmail.com> - 2011-04-06 08:41 -0700
    Re: TypeError: iterable argument required Νικόλαος Κούρας <nikos.kouras@gmail.com> - 2011-04-06 08:57 -0700
      Re: TypeError: iterable argument required Blockheads Oi Oi <breamoreboy@yahoo.co.uk> - 2011-04-06 17:12 +0100

#2704 — Re: TypeError: iterable argument required

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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#2706

On 6 Απρ, 16:54, "eryksun ()" <eryk...@gmail.com> wrote:

> You can also use an empty string as the default value when getting the field value

Please provide me an example.

> 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 ''.


>>> mail = None
>>> mail
>>> mail = mail or ''
>>> mail
''

Why in 2nd case the returned value of mail is None. Why shouldn't it
be the empty string since mail = None which is false.

How exactly Python parses those two statements in english words?

>>> mail = None
>>> mail
>>> mail = '' or mail
>>> mail
>>>



> 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.

Can you please also provide an example of what happens if i use the
special formatting identidier `%` instead of a comma?

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#2707

>>> mail = None
>>> mail = mail or 7
>>> mail
7

>>> mail = None
>>> mail = 7 or mail
>>> mail
7

Here no matter the order iam writing the comparison it always return
the number.

why not the same here?

>>> mail = None
>>> mail = mail or ''
>>> mail
''

>>> mail = None
>>> mail = '' or mail
>>> mail
>>>

Why the or operator behaves differently with numbers than from
strings?

Please explain to me how it parses it with words.

Thank you.

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#2708

On 06/04/2011 16:57, Νικόλαος Κούρας wrote:
>>>> mail = None
>>>> mail = mail or 7
>>>> mail
> 7
>
>>>> mail = None
>>>> mail = 7 or mail
>>>> mail
> 7
>
> Here no matter the order iam writing the comparison it always return
> the number.
>
> why not the same here?
>
>>>> mail = None
>>>> mail = mail or ''
>>>> mail
> ''
>
>>>> mail = None
>>>> mail = '' or mail
>>>> mail
>>>>
>
> Why the or operator behaves differently with numbers than from
> strings?
>
> Please explain to me how it parses it with words.
>
> Thank you.

See this for an explanation of Python truth value testing.
http://docs.python.org/library/stdtypes.html

Cheers.

Mark L.

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