Hello matplotlib users!

I 'm using matplotlib for one week and I 'm excited.
The only thing I couldn't do is to save image's contect straightway to SQL server. So I 'm searching for a function that store figure's image as binary data in a python variable in order to put the content of this variable inside an postgresql query.

For example:
.......
matplotlib code
.........
conn = psycopg2.connect(.......)
curs = conn.cursor()
image_data=###The matplotlib function I'm searching###
sql = "update med_graphs set image=%s;"
curs.execute(sql,image_data,))
conn.commit()

I found only the figure.savefig() function that saves figure's image only as a filename in the filesystem and not in a local variable.

Any help would very much appreciated!
Panagiotis