Decorator indicating a method is both a class and an instance method
pip install combomethod==1.0.12
Python has instance methods, class methods (@classmethod
), and static
methods (@staticmethod
). But it doesn't have a clear way to invoke a method
on either a class or its instances. With combomethod
, it does.
from combomethod import combomethod class A(object): @combomethod def either(receiver, x, y): return x + y a = A() assert a.either(1, 3) == 4 assert A.either(1, 3) == 4
Voila! You method now takes either the class or the instance--whichever one you want to call it with.
In some cases, you can fake @combomethod
with @classmethod
. In
the code above, for example, there is no real reference to the class
or instance, and either
could have been designated a @classmethod
,
since they can be called with either classes or instances. But, there's a
problem: Class methods always pass the class to the method, even if they're
called with an instance. With this approach, you can never access the
instance variables. Ouch!
Alternatively, either
could have been designated a @staticmethod
,
had its receiver
parameter been removed. But while it would then be
callable from either an instance or a class, in neither case would it pass
the object the method was called from. There'd never be a way to access
either the class or instance variables. Ouch again!
As useful as @classmethod
and @staticmethod
are, they don't handle the
(occasionally important) corner case where you need to call with either the
class or an instance and you need genuine access to the object doing the
call. Here's an example that needs this:
class Above(object): base = 10 def __init__(self, base=100): self.base = base @combomethod def above_base(receiver, x): return receiver.base + x a = Above() assert a.above_base(5) == 105 assert Above.above_base(5) == 15 aa = Above(12) assert aa.above_base(5) == 17 assert Above.above_base(5) == 15
When you need to call with either an instance or a class, and you also care
about the object doing the calling, @combomethod
rocks and rolls.
CHANGES.yml
for the complete Change Log.To install or upgrade to the latest version:
pip install -U combomethod
You may need to prefix these with sudo
to authorize installation. In
environments without super-user privileges, you may want to use pip
's
--user
option, to install only for a single user, rather than system-wide.
You may also need Python-version-sepecific pip2
or pip3
installers,
depending on your system configuration. In cases where pip
isn't
well-configured for a specific Python instance you need, a useful fallback:
python3.6 -m pip install -U combomethod