Friday, March 13, 2009

pyodbc doesn't seem to like BLOBs

I tried to pull a Binary Large OBject out of a SQL Server database yesterday via pyodbc, and it blew up.

In [4]: c = pyodbc.connect('DRIVER={SQL Server};SERVER=servername;')
In [5]: r = c.execute('select Blob from dbo.tbDoc where DocID = 8')
In [6]: row = r.fetchone()
assertion failed: getdata.cpp(171)
cbRead == 0 || pch[cbRead-element_size] != 0

And crashed my IPython shell, to boot.

Python's DB API spec (aka PEP 249) doesn't appear to specify exactly how to handle BLOBs, but it does mention them, so I presume they're supposed to be supported. I wound up grabbing this particular BLOB in a C# app instead, but this seems like it could be an issue in the future, so if anyone knows what's going on, please let me know. Otherwise I'll dig into this issue next time I have some spare time or a pressing need to manipulate BLOBs in Python.

UPDATE: I wasn't on the latest build of pyodbc, so I updated to 2.1.3. After updating, I was able to fetch the binary stream from that row. Hooray!

Although when attempting to print it out, I got some weird behavior - my PC's internal speaker started beeping like mad and the window stopped responding. As my colleague said:

P.V. [1:57 PM]:
What the hell was stored in that blob?
Ira Pfeifer [1:58 PM]:
just a hex stream
P.V. [1:58 PM]:
This is like something from Gibson.


1 comment:

Scott Mahr said...

Have you tried loading binary data (an image) into a db with pyodbc? I have been working at it for a day or two, and can't figure it out. Found there is a pyodbc.Binary function that should help, but not luck so far. Any help with that would be awesome, thanks