Delays getting data on sys.stdin.readline() ?

[Christian Convey]

Hello,

I've got a program that (ideally) perpetually monitors sys.stdin for
lines of text. As soon as a line comes in, my program takes some
action.

The problem is, it seems like a very large amount of data must
accumulate on sys.stdin before even my first invocation of readline()
returns.  This delay prevents my program from being responsive in the
way it must be.

Has anyone else seen this effect?  If so, is there a reasonable workaround?

Thanks very much,
Christian