There is a similar question, but it doesn't explicitly answer my question: is there a way to have an init/constructor function which will be automatically called just ONCE among all class instances so that to initialize class variables?
class A:
_config = None
#load the config once for all instances
@classmethod
def contstructor(cls):
cls._config = configparser.ConfigParser()
cls._config.read("config_for_A.ini")
This is called the "Orcish Maneuver". It does assume that the "cache" can be evaluated as a Boolean.
class A:
_config = False
#load the config once for all instances
@classmethod
def contstructor(cls):
cls._config = configparser.ConfigParser()
cls._config.read("config_for_A.ini")
def __init__(self):
self._config = self._config or self.contstructor()
hay = A()
bee = A()
sea = A()
There are no magic methods for class constructors, but Python executes all code inside a class definition that does not belong to methods when parsing the class. So you can either perform your actions and assignments there directly or call a custom method of your class from there that serves as class constructor.
print("Now defining class 'A'...")
class A:
# define any initialization method here, name is irrelevant:
def __my_class_constructor():
print("--> class initialized!")
# this is the normal constructor, just to compare:
def __init__(self):
print("--> instance created!")
# do whatever you want to initialize the class (e.g. call our method from above)
__my_class_constructor()
print("Now creating an instance object 'a' of class 'A'...")
a = A()
The output will be:
Now defining class 'A'...
--> class initialized!
Now creating an instance object 'a' of class 'A'...
--> instance created!
if cls._config is None, or look into metaclasses, or just doclass A: _config = some_config_parser().