No it doesn't. The problem is that using a connection as a context
manager doesn't do what you think.
It does *not* start a new transaction on __enter__ and commit it on
__exit__. As far as I can tell it does nothing on __enter__ and calls
con.commit() or con.rollback() on exit. With isolation_level=None,
these are no-ops.
Thank you Ryan! You are abolutely right, and thank you for reading the
source. Now everything works as I imagined.
The way the context manager and isolation_level works looks very very
strange to me. Here is a demonstration:
import sqlite3
def getconn():
conn = sqlite3.connect(':memory:')
conn.isolation_level = None
return conn
def main():
with getconn() as conn:
conn.execute("create table a ( i integer ) ")
try:
conn.execute("insert into a values (1)")
with conn:
conn.execute("insert into a values (2)")
raise Exception
except:
print "There was an error"
for row in conn.execute("select * from a"):
print row
main()
Output:
There was an error
(1,)
(2,)
Looks like the context manager did not roll back anything. If I remove
isolation_level=None then I get this:
There was an error
E.g. the context manager rolled back something that was executed outside
the context. I cannot argue with the implementation - it is that way.
But this is not what I would expect. I believe I'm not alone with this.
Using your connection manager, everything is perfect:
There was an error
(1,)
The only thing I have left is to implement a connection manager that
emulates nested transactions, using a stack of savepoints. :-)
Suggestions:
Just for clarity, we should put a comment at the end of the
documentation here:
http://docs.python.org/library/sqlite3.html#sqlite3-controlling-transactions
I would add at least these things:
#1. By using isolation_level = None, connection objects (used as a
context manager) WON'T automatically commit or rollback transactions.
#2. Using any isolation level, connection objects WON'T automatically
begin a transaction.
#3. Possibly, include your connection manager class code, to show how to
do it "the expected" way.
Also one should clarify in the documentation, what isolation_level does.
Looks like setting isolation_level to None is not really an "auto commit
mode". It is not even part of sqlite itself. It is part of the python
extension.
Thank you again.
Laszlo
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