Setting a class attribute with a given name in python while defining the class

Question

I am trying to do something like this:

property = 'name'
value = Thing()
class A:
  setattr(A, property, value)
  other_thing = 'normal attribute'

  def __init__(self, etc)
    #etc..........

But I can't seem to find the reference to the class to get the setattr to work the same as just assigning a variable in the class definition. How can I do this?

Answer 1

You'll need to use a metaclass for this:

property = 'foo'
value = 'bar'

class MC(type):
  def __init__(cls, name, bases, dict):
    setattr(cls, property, value)
    super(MC, cls).__init__(name, bases, dict)

class C(object):
  __metaclass__ = MC

print C.foo

Answer 2

You can do it even simpler:

class A():
    vars()['key'] = 'value'

In contrast to the previous answer, this solution plays well with external metaclasses (for ex., Django models).

Answer 3

This may be because the class A is not fully initialized when you do your setattr(A, p, v) there.

The first thing to try would be to just move the settattr down to after you close the class block and see if that works, e.g.

class A(object):
    pass


setattr(A, property, value)

Otherwise, that thing Ignacio just said about metaclasses.

Answer 4

So I know this is really old and probably beating a dead horse and this may not have been possible at the time but I cam across this trying to solve my own problem.

I realized this can be accomplished without metaclassing.

The setattr takes and object, accessor name, and value. Well the object is not the class name it's the specific instance of the class, which can be accomplished with self.

class A(object):
    def __init__(self):
        self.a = 'i am a accessor'
        setattr(self, 'key', 'value')

a = A()
print a.a
print a.key