Pythonic ways of traversing imported constants

Question

I'm importing some constants from my file constants.py like this:

from constants import (SOME_CONST, OTHER_CONST, ANOTHER_ONE)

This constants are filenames and I'm reading data out of them, what I want to achieve is this:

for filename in [SOME_CONST, OTHER_CONST, ANOTHER_ONE]:
    # process file

constants.py

SOME_CONST = "filename.txt"
OTHER_CONST = "myfile.xml"
ANOTHER_ONE = "file.csv"

But I want to know if there is a way to avoid declaring the list in the for, like traverse or build a list of imported constants, because there can be many constants not just 3 like the example and it is error prone, since I would need to import the constant and add it to the list, I just want to import it and work with whatever is imported.

Answer 1

You cannot list 'all imported constants', no. They are just more globals in your current module.

Your options are to:

1. list all names on the constants module:

   import constants
   
   for name in dir(constants):
       const = getattr(constants, name)
   

   You can filter those names if they follow a pattern:

   for name in dir(constants):
       if name.startswith('FOO_'):
   

   The filter can be a simple as checking that the name is all uppercase.

2. declare the list as part of your constants module, and import that instead.

3. declare a list of names in your current module, and use that to 'import' your constants:

   import constants
   
   const_names = ['SOME_CONST', 'OTHER_CONST', 'ANOTHER_ONE']
   for const_name in const_names:
       const = getattr(constants, const_name)