Pass Variable On Import

Question

Let\'s say you have some time-consuming work to do when a module/class is first imported. This functionality is dependent on a passed in variable. It only needs to be done

Answer 1

I had to do something similar for my project. If you don't want to rely on the calling script to run the initialization function, you can add your own Python builtin which is then available to all modules at runtime.

Be careful to name your builtin something unique that is unlikely to cause a namespace collision (eg myapp_myvarname).

run.py

import __builtin__
__builtin__.myapp_PATH_TO_R_SOURCE = 'path.to.r.source'
import someClass

someClass module .py

import rpy2.robjects as robjects
import __builtin__

if hasattr(__builtin__, "myapp_PATH_TO_R_SOURCE"):
    PATH_TO_R_SOURCE = __builtin__.myapp_PATH_TO_R_SOURCE
else:
    PATH_TO_R_SOURCE = ## Some default value or Null for Exception handling
robjects.r.source(PATH_TO_R_SOURCE, chdir = True)

...

This works well for variables that may have a default but you want to allow overriding at import time. If the __builtin__ variable is not set, it will use a default value.

Edit: Some consider this an example of "Monkey patching". For a more elegant solution without monkey patch, see my other answer.