BLOB columns are converted to/from UTF8 about apsw HOT 11 CLOSED

From rogerbinns on July 17, 2008 13:24:31

Since you are supplying a Python string, it has to be converted to Unicode since that
is the only type of string that SQLite accepts. (This is before any column affinity
rules are applied by SQLite).

To supply binary data use the buffer class - in your example:

buffer("\xcf\xde")

I will update the documentation section Types to be a little clearer as well as add
something to the example.

Status: Accepted
Labels: Component-Docs

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From [email protected] on July 18, 2008 03:32:57

I'm afraid this doesn't work for me:

c.execute("insert into blobs values(?)", buffer("\xFE"))
Traceback (most recent call last):
File "", line 1, in
UnicodeDecodeError: 'ascii' codec can't decode byte 0xfe in position 0: ordinal not
in range(128)

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From rogerbinns on July 18, 2008 03:38:05

That is because you are not providing a tuple of items like in your first post :-)
It should be:

c.execute("insert into blobs values(?)", (buffer("\xFE"), ) )

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From [email protected] on July 18, 2008 10:39:19

True, now it works indeed. Thanks a lot!

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From [email protected] on July 18, 2008 10:49:21

This might be a stupid question, but how can I get back a (byte) string from the
buffer that I get when I query the table?

I couldn't find any documentation of the buffer objects on python.org/doc...

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From rogerbinns on July 18, 2008 13:15:44

In Python 2 you can turn a buffer into a string by using str or [:]. For example:

x=buffer("abc")
print type( str(x) )
print type( x[:] )

If you look in the index in the Python documentation you'll find some measly doc.

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From [email protected] on July 19, 2008 01:34:22

Your example works nicely, but for some reason it does not work if I apply it to the
buffer object returned by the cursor:

c.execute("insert into blobs values(?)", (buffer("\xCF"),))
<apsw.Cursor object at 0xb7db6d10>
res = c.execute("select * from blobs")
a = res.next()
a
(<read-write buffer ptr 0xb7db8d10, size 1 at 0xb7db8cf0>,)
str(a)
'(<read-write buffer ptr 0xb7db8d10, size 1 at 0xb7db8cf0>,)'

I'm using Python 2.5.2

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From rogerbinns on July 19, 2008 01:37:43

The cursor iterator returns an entire row as a tuple. You called str on that so that
is exactly what you have printed out - a tuple containing one buffer item.

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From [email protected] on July 19, 2008 01:55:19

Brrr... You're of course right again. I probably shouldn't try to learn Python and
apsw at the same time. Thanks a lot for your help and patience!

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From rogerbinns on July 19, 2008 02:47:17

There is no problem learning Python and APSW at the same time. Python itself is very
simple although it takes a while to learn "best practise". The paper version of the
Python Cookbook is a good tour of various best practises.

Your "mistake" is assuming that whenever you encounter issues they are bugs. The
chances of you finding bugs in Python, APSW, SQLite etc after just starting using
them is extremely low compared to the underlying issue being in your code or
understand of how things work :-)

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From rogerbinns on July 26, 2008 02:47:44

Doc updated in r190

Status: Verified

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