Read binary data from MySQL database

[Christoph Krammer]

Hello,

I try to write a python application with wx that shows images from a
MySQL database. I use the following code to connect and get data when
some event was triggered:

dbconn = MySQLdb.connect(host="localhost", user="...", passwd="...",
db="images")
dbcurs = dbconn.cursor()
dbcurs.execute("""SELECT imgdata FROM images LIMIT 1""")
imgstring = dbcurs.fetchone()[0]
frame.showImage(imgstring)

Within my frame, the following method is defined:

def showImage(self, imgstring):
imgdata = StringIO.StringIO()
imgdata.write(imgstring)
print imgdata.getvalue()
wx.ImageFromStream(imgdata, wx.BITMAP_TYPE_GIF)
panel = wx.Panel(self, -1)
self.panel = panel

But this does not work. The converter says that the data is not valid
GIF. When I print the content of imgstring after the database select
statement, it contains something like this:

array('c', 'GIF89aL\x01=\x01\x85\x00\x00\x00\x00\x00\xff\xff\ xff
\x00\xff\xff\xff[...]\x00\x00;')

When I try to print imgstring[1], the result is "I". So I don't quite
get what this print result is about and why my input should not be
valid. The data in the database is correct, I can restore the image
with tools like the MySQL Query Browser.

Thanks in advance,
Christoph

[Carsten Haese]

On Thu, 2007-05-10 at 07:19 -0700, Christoph Krammer wrote:

Hello,

I try to write a python application with wx that shows images from a
MySQL database. I use the following code to connect and get data when
some event was triggered:

dbconn = MySQLdb.connect(host="localhost", user="...", passwd="...",
db="images")
dbcurs = dbconn.cursor()
dbcurs.execute("""SELECT imgdata FROM images LIMIT 1""")
imgstring = dbcurs.fetchone()[0]
frame.showImage(imgstring)

Within my frame, the following method is defined:

def showImage(self, imgstring):
imgdata = StringIO.StringIO()
imgdata.write(imgstring)
print imgdata.getvalue()
wx.ImageFromStream(imgdata, wx.BITMAP_TYPE_GIF)
panel = wx.Panel(self, -1)
self.panel = panel

But this does not work. The converter says that the data is not valid
GIF. When I print the content of imgstring after the database select
statement, it contains something like this:

array('c', 'GIF89aL\x01=\x01\x85\x00\x00\x00\x00\x00\xff\xff\ xff
\x00\xff\xff\xff[...]\x00\x00;')

That means that imgstring is not a string, it's an array of characters.
Observe:

>>import array
a = array.array('c', 'Blahblahblah')
print a

array('c', 'Blahblahblah')

>>str(a)

"array('c', 'Blahblahblah')"

>>a.tostring()

'Blahblahblah'

Calling write() with an object that's not a string will implicitly call
str() on that object and write the result of that call to the file. Try
imgdata.write(imgstring.tostring()) to extract the string data from the
array.

Hope this helps,

--
Carsten Haese
http://informixdb.sourceforge.net

[Stefan Sonnenberg-Carstens]

On Do, 10.05.2007, 16:19, Christoph Krammer wrote:

Hello,

I try to write a python application with wx that shows images from a
MySQL database. I use the following code to connect and get data when
some event was triggered:

dbconn = MySQLdb.connect(host="localhost", user="...", passwd="...",
db="images")
dbcurs = dbconn.cursor()
dbcurs.execute("""SELECT imgdata FROM images LIMIT 1""")
imgstring = dbcurs.fetchone()[0]
frame.showImage(imgstring)

Within my frame, the following method is defined:

def showImage(self, imgstring):
imgdata = StringIO.StringIO()
imgdata.write(imgstring)

Use
imgdata.write(imgstring.tostring())
or
imgstring.tofile(imgdata)

print imgdata.getvalue()
wx.ImageFromStream(imgdata, wx.BITMAP_TYPE_GIF)
panel = wx.Panel(self, -1)
self.panel = panel

But this does not work. The converter says that the data is not valid
GIF. When I print the content of imgstring after the database select
statement, it contains something like this:

array('c', 'GIF89aL\x01=\x01\x85\x00\x00\x00\x00\x00\xff\xff\ xff
\x00\xff\xff\xff[...]\x00\x00;')

When I try to print imgstring[1], the result is "I". So I don't quite
get what this print result is about and why my input should not be
valid. The data in the database is correct, I can restore the image
with tools like the MySQL Query Browser.

Thanks in advance,
Christoph

--
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