Where to put constants in python

Question

I'm very new to python and would like to understand what is the pythonic way to define some contants. I have the following class:

class ConfigBuilder:

   def add_param(self, key, value):
       #...
   def build():
       #...

Now I want to use this in another module as follows:

some_val = #...
config_builder builder = ConfigBuilder()
builder.add_param('PROJECT_RELATED_KEY', some_val)

Where to put this 'PROJECT_RELATED_KEY'? In another module and then import it? Or put it as a global variable?

Answer 1

Agreed that there is no absolute convention for where settings should be stored. There's a lot of flexibility when it comes to project placement. Below are a few possibilities I might consider when deciding where to put my own settings.

If your project might contains some sensitive parameters that you wouldn't want in version control, you could put them into your environment and then access them with environment variables.

import os
print os.environ['HOME']

If they're not sensitive at all, one possible route would be to do what Django does and create a settings.py file. Something like this

# myproject/settings.py
SOME_VALUE = 'SomeConfigurableValue'
FOO = 'bar'
PROJECT_RELATED_KEY = 'bestkeyever'

# myproject/builder.py
from myproject.settings import SOME_VALUE
print(SOME_VALUE)

You could even set up the project as a package and then do

from . import settings
print(settings.SOME_VALUE)

For more info on setting up a project as a package, see: How to fix "Attempted relative import in non-package" even with __init__.py