Should -R be required to take a parameter specifying "on" or "off" so that code using a #! line continues to work as specified across the a change in default behavior when upgrading from 3.2 to 3.3? #!/usr/bin/python3 -R on #!/usr/bin/python3 -R off In 3.3 it would be a good idea to have a command line flag to turn this off. Rather than introducing a new flag in 3.3 a parameter that is specific without regards for the default avoids that entirely. before anyone suggests it: I do *not* think -R should accept a value to use as the seed. that is unnecessary.