Creating a Static Class with No Instances
All of the Tutorials I See Online Show How to Create Classes with __Init__ Constructor Methods So One Can Declare Objects of That Type, or Instances of That...
All of the tutorials I see online show how to create classes with __init__ constructor methods so one can declare objects of that type, or instances of that class.
How do I create a class (static in Java) so that I can access all methods and attributes of that class without having to create new instances/objects?
For example:
class World:
allElems = []
def addElem(x):
allElems.append(x)
World.addElem(6)
print(World.allElems)
EDIT
class World(object):
allAirports = []
@staticmethod
def initialize():
f = open(os.path.expanduser("~/Desktop/1000airports.csv"))
file_reader = csv.reader(f)
for col in file_reader:
allAirports.append(Airport(col[0],col[2],col[3]))
error: name 'allAirports' is not defined
5 Answers
The Pythonic way to create a static class is simply to declare those methods outside of a class (Java uses classes both for objects and for grouping related functions, but Python modules are sufficient for grouping related functions that do not require any object instance). However, if you insist on making a method at the class level that doesn't require an instance (rather than simply making it a free-standing function in your module), you can do so by using the "@staticmethod" decorator.
That is, the Pythonic way would be:
# My module
elements = []
def add_element(x):
elements.append(x)
But if you want to mirror the structure of Java, you can do:
# My module
class World(object):
elements = []
@staticmethod
def add_element(x):
World.elements.append(x)
You can also do this with @classmethod if you care to know the specific class (which can be handy if you want to allow the static method to be inherited by a class inheriting from this class):
# My module
class World(object):
elements = []
@classmethod
def add_element(cls, x):
cls.elements.append(x)
You could use a classmethod or staticmethod
class Paul(object):
elems = []
@classmethod
def addelem(cls, e):
cls.elems.append(e)
@staticmethod
def addelem2(e):
Paul.elems.append(e)
Paul.addelem(1)
Paul.addelem2(2)
print(Paul.elems)
classmethod has advantage that it would work with sub classes, if you really wanted that functionality.
module is certainly best though.
There are two ways to do that (Python 2.6+):
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