What's the best way to initialise and use constants across Python classes?
PythonPython Problem Overview
Here's how I am declaring constants and using them across different Python classes:
# project/constants.py
GOOD = 1
BAD = 2
AWFUL = 3
# project/question.py
from constants import AWFUL, BAD, GOOD
class Question:
def __init__(self):
...
Is the above a good way to store and use contant values? I realise that after a while, the constants file can get pretty big and I could explicitly be importing 10+ of those constants in any given file.
Python Solutions
Solution 1 - Python
why not just use
import constants
def use_my_constants():
print constants.GOOD, constants.BAD, constants.AWFUL
From the python zen:
> Namespaces are good. Lets do more of those!
EDIT: Except, when you do quote, you should include a reference and check it, because as others have pointed out, it should read:
> Namespaces are one honking great idea -- let's do more of those!
This time, I actually copied it from the source: PEP 20 -- The Zen of Python
Solution 2 - Python
You also have the option, if the constants are tied to a particular class and used privately within that class of making them specific to that class:
class Foo(object):
GOOD = 0
BAD = 1
WTF = -1
def __init__(self...
and away you go.
Solution 3 - Python
You have a few options:
- Do it the way you're doing right now with a file of constants
- Use a flat file and parse it once, pass a dictionary / class around
- Query off to a database
From an overhead point of view, 1 and 2 are about the same. As for your question about importing specific constants, it's much easier to use one of the following conventions:
import constants; some_func(constants.AWFUL)from constants import *; some_func(AWFUL)
Solution 4 - Python
Try to look at the following links(one link contains a receipt from active state of how to implement a real constants):
https://stackoverflow.com/questions/6343330/importing-a-long-list-of-constants-to-a-python-file
https://stackoverflow.com/questions/3824455/python-constants
https://stackoverflow.com/questions/3711657/can-i-prevent-modifying-an-object-in-python