blob problems in pysqlite

[Gerhard Häring]

aldonnelley at gmail.com wrote:
> Excellent. Got that working. Now, how to get the pickled data out of
> the database?
> 
> I'm trying to use cPickle.loads(data) (code attached), and I get a:
> "TypeError: loads() argument 1 must be string, not list" [...]
> [...]
> c.execute("select Images from FileURLInfo where URL= ?;", (DBURL,))
> KnownFilesResult = c.fetchall()
> print KnownFilesResult    #where I get a r/w buffer, as expected

No, you actually get a list of 1-tuples and each tuple has one entry: a 
read-write buffer. Because of the way you filled the table, the list is 
of length 1.

> cPickle.loads(KnownFilesResult)    #where I get the error described
> above.

cPickle.loads will only accept a string, not a buffer, so you need to 
convert the buffer to a string first.

So, if you want your code to work, you can use

print cPickle.loads(str(KnownFilesResult[0][0]))

FWIW there are certainly much better ways to solve the task you're 
solving here. Because right now you're pickling and unpickling data into 
a single table in a relational database. Like you're doing this, this 
buys you nothing *and* you get the complexity of relational databases 
and object (de)marshaling.

If you want to go the relational way, you can create multiple tables and 
using foreign-key relations between them instead of stuffing lists into 
columns of a single table by pickling them.

I've attached an example script that can perhaps inspire you.

-- Gerhard
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