Question

I manage a fairly large python-based quantum chemistry suite, PyQuante. I’m currently struggling with how to set various defaults so that users can choose among different options at runtime.

For example, I have three different methods for computing electron repulsion integrals. Let’s call them a,b,c. I used to simply pick the one I liked best (say, c), and have that hard-wired into the module that computes these integrals.

I have now modified this to use a module, Defaults.py, that contains all such hard-wires. But this is set at compile/install time. I would now like users to be able to override these options at runtime, say, using a .pyquanterc.py file.

In my integral routines, I currently have something like

from Defaults import integral_method

I know about dictionaries, and the .update() method. But I don’t know how I would use this in real life. My defaults module looks like

integral_method = c

should I modify the end of Defaults.py to look for a .pythonrc.py file and override these values? E.g.

if os.path.exists('$HOME/.pythonrc.py'): do_something

If so, what should do_something look like?

Answer 1

With your current setup, the user can change the default functions in his scripts quite easily:

import Defaults
Defaults.integral_method = somefunc

If the user adds this to his script, all your modules that use integral_method from Defaults will use somefunc to calculate integrals.