I have found a data corruption problem with pyodbc.
OS = Windows XP SP2
DB = Microsoft Access XP
PROBLEM:
When selecting columns from a table that are of type Memo the value
returned is padded with a bunch of null characters at the end.
The problems does not seem to occur until the length of the Memo column
exceeds 2048 bytes.
I have attached several scripts to help demonstrate the problem.
To recreate the problem:
1. Create a blank Access database named test.
2. Create a ODBC DSN named test for that database
3. Run the createtable.py script to create the table
and load it with the dummy data
4. Run the broke.py script to show the problem.
The issue is when the data value is > 2048 bytes.
The size in the createtable.py is 2046 bytes plus 3 bytes at the end that
contain "JOE" for a total of 2049 bytes.
If you change it from 2046 to 2045 (or less) then the problem does not
occur.
#
# createtable.py script
#
import pyodbc
dbs = pyodbc.connect('dsn=test')
c = dbs.cursor()
try:
sql = 'drop table test_memo'
c.execute(sql)
dbs.commit()
except:
# ignore drop table failure
pass
sql = 'create table test_memo (c1 int not null, c2 memo not null)'
c.execute(sql)
dbs.commit()
sql = 'insert into test_memo values(1, ?)'
c2_value = '1' * 2046
c2_value = '%sJOE' % (c2_value)
c.execute(sql, (c2_value,))
dbs.commit()
c.close()
dbs.close()
#
# broke.py script
#
import pyodbc
dbs = pyodbc.connect('dsn=test')
c = dbs.cursor()
sql = 'select c2, len(c2) as c2_db_len from test_memo where c1 = 1'
c.execute(sql)
row = c.fetchone()
(
c2,
c2_db_len
) = row
print repr(c2)
print 'c2 length :', len(c2)
print 'c2_db_length :', c2_db_len
print 'before nul length:', len(c2[0:c2.find('\x00')])
c.close()
dbs.close()
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