Python style: exceptions vs. sys.exit()

[Drake]

I have a general question of Python style, or perhaps just good
programming practice.

My group is developing a medium-sized library of general-purpose
Python functions, some of which do I/O. Therefore it is possible for
many of the library functions to raise IOError Exceptions. The
question is: should the library function be able to just dump to
sys.exit() with a message about the error (like "couldn't open this
file"), or should the exception propagate to the calling program which
handles the issue?

Thanks in advance for anyone who can either answer my question or
point me to where this question has already been answered.