I am writing an object-oriented app to help our developers manage some cloud systems. I’d like to make the configuration information available to all the classes, but I’m not sure of a good way to do that. Everything I can think of seems to fall under the category of “global variables” which as far as I know is a Very Bad Thing.
I already have a logging Mixin class that enables logging for every class that inherits it, and I was wondering if that’s the right way to approach the configuration data:
class LoggingMixin:
@classmethod
@property
def log(cls):
return logging.getLogger(cls.__name__)
class TestClassA(LoggingMixin):
def testmethod1(self):
self.log.debug("debug message from test class A")
if __name__ == "__main__":
logging.basicConfig(
format="{created:<f} {levelname:>5s} {name}.{funcName:>8s} |{message}|",
level=logging.DEBUG,
style="{",
)
a = TestClassA()
a.testmethod1()
Outputs (in case you are curious)
1688494741.449282 DEBUG TestClassA.testmethod1 |debug message from test class A|
What’s a good way of making data from a class available to all classes/objects? It wouldn’t be static, it’d be combined from a JSON file and any command line parameters.
If I copied the example above but changed it to a ConfigMixin, would that work? With the logging example, each class creates its own logger object when it first calls self.log.debug, so that might not work because each object needs to get the same config data.
Is there a pattern or other design that could help? How do you make configuration data available to your whole app? Do you have a config object that can get/set values and saves to disk, etc?
Thank you for reading, my apologies for poorly worded questions.
I use a singleton class called Config (some times I use it as a Cache too)
Singleton pattern: https://www.geeksforgeeks.org/singleton-pattern-in-python-a-complete-guide/
Config class using Singleton pattern: https://charlesreid1.github.io/a-singleton-configuration-class-in-python.html
I don’t see why you need a singleton, just use use a global variable if you really need one. A singleton has all the same downsides but just hides them by not looking like a global.
https://nedbatchelder.com/blog/202204/singleton_is_a_bad_idea.html
You can use global variables, it is true, but I prefer singleton because I have all config variables and logic encapsulated in a class. The first time the singleton object is created it reads all the config variables from a file, and with its methods get and set manages them. The Config class doesn’t know the parameters names of the config file neither the number, it dynamically reads the file and creates the attributes, so It is a very reusable code that when you program using OOP is a more natural way than implementing like a module.
Related to this, I group config variables by sections so it is more clearly for me, then the singleton object dynamically creates an array for each section, and a variable into the array for every variable in this section of the config file. Access to the config info is as easy like this:
conf = Config() conf.get('DB', 'server') conf.get('DB', 'login') conf.get('DB', 'password')This is great, thank you! I’ll look at implementing this soon.