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Hello

I use regexes to extract information from a text file. Some of the
records don't have e-mails or www addresses, so those must match Null
in SQL, but None doesn't work as expected:

=======
if itemmatch:
web = itemmatch.group(1).strip()
else:
web = None

sql = 'INSERT INTO mytable (name,address,web,mail) VALUES
("%s","%s","%s","%s","%s")' % (name,address,web,mail)
=======

Is there a better way in Python to have a variable match NULL than
building the SQL query step by step?

Thank you.

Hi,

I'd create a simple wrapper object

class MailAddress(object):
def __init__(self, address=None):
self.address = address
def __str__(self):
if address:
return self.adress
return "NULL"

you can keep most of your code just replace the original instantiation
of the mail str-instance with the MailAddress

This is just scratched up quickly. Hope it helps

Martin

2008/12/26 Gilles Ganault <>:
> sql = 'INSERT INTO mytable (name,address,web,mail) VALUES
> ("%s","%s","%s","%s","%s")' % (name,address,web,mail)
> =======
>
> Is there a better way in Python to have a variable match NULL than
> building the SQL query step by step?
>
> Thank you.
> --
> http://mail.python.org/mailman/listinfo/python-list
>



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On Dec 27, 7:33*am, Gilles Ganault <nos...@nospam.com> wrote:
> Hello
>
> I use regexes to extract information from a text file. Some of the
> records don't have e-mails or www addresses, so those must match Null
> in SQL, but None doesn't work as expected:
>
> =======
> * * * * if itemmatch:
> * * * * * * * * web = itemmatch.group(1).strip()
> * * * * else:
> * * * * * * * * web = None
>
> * * * * sql = 'INSERT INTO mytable *(name,address,web,mail) VALUES
> ("%s","%s","%s","%s","%s")' % (name,address,web,mail)
> =======

You have MULTIPLE problems here.

PROBLEM 1:
That code won't even create the "sql" string; you have %s 5 times, but
only 4 elements in the tuple. When asking for help, always post (1)
the code that you actually ran (2) the result or error message that
you got [merely saying "doesn't work" is not very useful at all].

PROBLEM 2:
Having fixed problem 1, the result is not valid SQL; you get VALUES
("Gilles", ...; it should be VALUES('Gilles', ...

PROBLEM 3:
Having fixed problem 2: If you have a name like "L'Hopital" or
"O'Reilly" the result is VALUES('L'Hopital', ...; it should be VALUES
('L''Hopital', ...

*AND* you don't have to worry about all the rules for SQL constant
values; the worrying and work has been done for you.

> Is there a better way in Python to have a variable match NULL than
> building the SQL query step by step?

Yes. Don't construct the SQL query by Python string formatting. In
fact, don't *ever* construct *any* SQL query that needs args by using
string formatting/interpolation in *any* language, even when you think
it's "working" -- see http://en.wikipedia.org/wiki/SQL_injection ...
search for "SQL injection attack" for more references.

Essential reference: the Python Database API Specification v2.0
(http://www.python.org/dev/peps/pep-0249/)

You need something like:
sql = "INSERT INTO mytable (name,address,web,mail) VALUES(?,?,?,?)"
cursor.execute(sql, (name, address, web, mail))

Some database software uses something other than ? to mark parameter
positions; you may need (for example) ... VALUES(%s,%s,%s,%s) ...
(*NOT* the same meaning as %s in Python!). Read about "paramstyle" in
the DB API spec, and check the documentation for the DB software that
you are using.

HTH,
John

On Dec 27, 8:16*am, Scott David Daniels <Scott.Dani...@Acm.Org> wrote:
> Martin wrote:
> > ...
> > class MailAddress(object):
> > * def __init__(self, address=None):
> > * * self.address = address
> > * def __str__(self):
> > * * if address:
> > * * * return self.adress
> > * * return "NULL"
>
> There is an obvious typo above:
> *> * * if address:
> should be:
> * * * *if self.address:
>
> Or, you could replace the __str__ function with:
> * * *def __str__(self):
> * * * * *return self.address or "NULL"

The above all have the same characteristic: if the input is a zero-
length string, then NULL is inserted into the database instead of a
zero-length string. Some folks (not just pedants!) regard that as an
important difference.

2008/12/26 John Machin <>:
> The above all have the same characteristic: if the input is a zero-
> length string, then NULL is inserted into the database instead of a
> zero-length string. Some folks (not just pedants!) regard that as an
> important difference.

agreed but I understood the OP specifically wanted NULL and not ''.

of course for data gathering in web apps I'd personally make the mail
attribute a NOT NULL and reject anybody who wouldn't give me their
mail address. After all mail is the way to get in touch with my
customers/user if they register on my site, and if it's only for a
password reset link.

/martin


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On Dec 27, 11:05*am, Martin <mar...@marcher.name> wrote:
> 2008/12/26 John Machin <sjmac...@lexicon.net>:
>
> > The above all have the same characteristic: if the input is a zero-
> > length string, then NULL is inserted into the database instead of a
> > zero-length string. Some folks (not just pedants!) regard that as an
> > important difference.
>
> agreed but I understood the OP specifically wanted NULL and not ''.

He wanted None inserted into the database as NULL if his regex didn't
match. He didn't invite you to change a matching '' to NULL with no
announcement.