Comment 1 for bug 760035

Ok, I have a tentative fix for this bug.

Here's my test sources.list before (containing both valid and invalid entries):

# Valid binary entries
deb http://ports.ubuntu.com/ubuntu-ports natty main restricted
deb http://ports.ubuntu.com/ubuntu-ports natty-security main restricted
deb http://ports.ubuntu.com/ubuntu-ports natty-updates main restricted

# Valid source entries
deb-src http://ports.ubuntu.com/ubuntu-ports natty main restricted
deb-src http://security.ubuntu.com natty-security main restricted
deb-src http://archive.ubuntu.com/ubuntu natty-updates main restricted

# Invalid binary entry
deb http://archive.ubuntu.com/ubuntu natty-proposed main restricted

After running the modified python-apt, I get:

# Valid binary entries
deb http://ports.ubuntu.com/ubuntu-ports natty main restricted universe multiverse
deb http://ports.ubuntu.com/ubuntu-ports natty-security main restricted universe multiverse
deb http://ports.ubuntu.com/ubuntu-ports natty-updates main restricted universe multiverse

# Valid source entries
deb-src http://ports.ubuntu.com/ubuntu-ports natty main restricted universe multiverse
deb-src http://security.ubuntu.com natty-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu natty-updates main restricted universe multiverse

# Invalid binary entry
deb http://archive.ubuntu.com/ubuntu natty-proposed main restricted