subprocess with shared environment?

[rowen]

I'd like to replace some shell scripts with Python, but one step of
the script modifies my environment in a way that the subsequent steps
require.

A simple translation to a few lines of subprocess.call(...) fails
because the first call modifies the environment, but the other lines
don't see it.

Is there a straightforward  way to do this (without having to resort
to writing some of it as a shell script)?

-- Russell