Re: Trouble writing to database: RSS-reader

Arne a écrit :
Hi!

I try to make a rss-reader in python just for fun, and I'm almost
finished.

Bad news : you're not.

I don't have any syntax-errors, but when i run my program,
nothing happends.

This program is supposed to download a .xml-file, save the contents in
a buffer-file(buffer.txt) and parse the file looking for start-tags.
When it has found a start tag, it asumes that the content (between the
start-tag and the end-tag) is on the same line,

Very hazardous assumption. FWIW, you can more safely assule this will almost never be the case. FWIW, don't assume *anything* wrt/ newlines when it comes to XML - you can even have newlines between two attributes of a same tag...

so then it removes the
start-tag and the end-tag and saves the content and put it into a
database.

The problem is that i cant find the data in the database! If i watch
my program while im running it, i can see that it sucsessfuly
downloads the .xml-file from the web and saves it in the buffer.

But I dont think that i save the data in the correct way, so it would
be nice if someone had some time to help me.

Full code: http://pastebin.com/m56487698
Saving to database: http://pastebin.com/m7ec69e1b
Retrieving from database: http://pastebin.com/m714c3ef8

1/ you don't need to make each and every variable an attribute of the class - only use attributes for what constitute the object state (ie: need to be maintain between different, possibly unrelated method calls). In your update_sql method, for exemple, beside self.connection and _eventually_ self.cursor, you don't need any attribute - local variables are enough.

2/ you don't need these <xxx>Stored variables at all - just reset title/link/description to None *when needed* (cf below), then test these variables against None.

3/ learn to use if/elif properly !-)

4/ *big* logic flaw (and probably the first cause of your problem): on *each* iteration, you reset your <xxx>Stored flags to False - whether you stored something in the database or not. Since you don't expect to have all there data on a single line (another wrong assumption : you might get a whole rss stream as one single big line), I bet you never write anything into the database .

5/ other big flaw : either use an autoincrement for your primary key - and *dont* pass any value for it in your query - or provide (a *unique*) id by yourself.

6/ FWIW, also learn to properly use the DB api - don't build your SQL query using string formatting, but pass the argument as a tuple, IOW:

# bad:
cursor.execute(
'''INSERT INTO main VALUES(null, %s, %s, %s)'''
% title, link, description
)

# good (assuming you're using an autoincrementing key for your id) :
cursor.execute(
"INSERT INTO main VALUES(<X>, <X>, <X>)",
(title, link, description)
)

NB : replace <X> with the appropriate placeholder for your database - cf your db module documentation (usually either '?' or '%s')

This will make the db module properly escape and convert values.

7/ str.replace() doesn't modify the string in-place (Python strings are immutable), but returns a new string. so you want:
line = line.replace('x', 'y')

8/ you don't need to explicitely call connection.commit on each and every statement, and you don't need to call it at all on SELECT statements !-)

9/ have you tried calling print_rss *twice* on the same instance ?-)

10/ are you sure it's useful to open the same 'buffer.txt' file for writing *twice* (once in __init__, the other in update_sql). BTW, use open(), not file().

11/ are you sure you need to use this buffer file at all ?

12/ are you really *sure* you want to *destroy* your table and recreate it each time you call your script ?

And yes, I know that there is rss-parseres already built, but this is
only for learning.

This should not prevent you from learning how to properly parse XML (hint: with an XML parser). XML is *not* a line-oriented format, so you just can't get nowhere trying to parse it this way.



HTH
.

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