Getting Attributes of a Class

Question

I want to get the attributes of a class, say:

class MyClass():
  a = "12"
  b = "34"

  def myfunc(self):
    return self.a

using MyClass.__dict__ gives me a list of attributes and functions, and even functions like __module__ and __doc__. While MyClass().__dict__ gives me an empty dict unless I explicitly set an attribute value of that instance.

I just want the attributes, in the example above those would be: a and b

Accepted Answer

Try the inspect module. getmembers and the various tests should be helpful.

EDIT:

For example,

class MyClass(object):
    a = '12'
    b = '34'
    def myfunc(self):
        return self.a

>>> import inspect
>>> inspect.getmembers(MyClass, lambda a:not(inspect.isroutine(a)))
[('__class__', type),
 ('__dict__',
  <dictproxy {'__dict__': <attribute '__dict__' of 'MyClass' objects>,
   '__doc__': None,
   '__module__': '__main__',
   '__weakref__': <attribute '__weakref__' of 'MyClass' objects>,
   'a': '34',
   'b': '12',
   'myfunc': <function __main__.myfunc>}>),
 ('__doc__', None),
 ('__module__', '__main__'),
 ('__weakref__', <attribute '__weakref__' of 'MyClass' objects>),
 ('a', '34'),
 ('b', '12')]

Now, the special methods and attributes get on my nerves- those can be dealt with in a number of ways, the easiest of which is just to filter based on name.

>>> attributes = inspect.getmembers(MyClass, lambda a:not(inspect.isroutine(a)))
>>> [a for a in attributes if not(a[0].startswith('__') and a[0].endswith('__'))]
[('a', '34'), ('b', '12')]

...and the more complicated of which can include special attribute name checks or even metaclasses ;)

Answer 2

def props(cls):   
  return [i for i in cls.__dict__.keys() if i[:1] != '_']

properties = props(MyClass)

Answer 3

Getting only the instance attributes is easy.
But getting also the class attributes without the functions is a bit more tricky.

Instance attributes only

If you only have to list instance attributes just use
for attribute, value in my_instance.__dict__.items()

>>> from __future__ import (absolute_import, division, print_function)
>>> class MyClass(object):
...   def __init__(self):
...     self.a = 2
...     self.b = 3
...   def print_instance_attributes(self):
...     for attribute, value in self.__dict__.items():
...       print(attribute, '=', value)
...
>>> my_instance = MyClass()
>>> my_instance.print_instance_attributes()
a = 2
b = 3
>>> for attribute, value in my_instance.__dict__.items():
...   print(attribute, '=', value)
...
a = 2
b = 3

Instance and class attributes

To get also the class attributes without the functions, the trick is to use callable().

But static methods are not always callable!

Therefore, instead of using callable(value) use
callable(getattr(MyClass, attribute))

Must Read

Example

from __future__ import (absolute_import, division, print_function)

class MyClass(object):
   a = "12"
   b = "34"               # class attributes

   def __init__(self, c, d):
     self.c = c
     self.d = d           # instance attributes

   @staticmethod
   def mystatic():        # static method
       return MyClass.b

   def myfunc(self):      # non-static method
     return self.a

   def print_instance_attributes(self):
     print('[instance attributes]')
     for attribute, value in self.__dict__.items():
        print(attribute, '=', value)

   def print_class_attributes(self):
     print('[class attributes]')
     for attribute in self.__dict__.keys():
       if attribute[:2] != '__':
         value = getattr(self, attribute)
         if not callable(value):
           print(attribute, '=', value)

v = MyClass(4,2)
v.print_class_attributes()
v.print_instance_attributes()

Note: print_class_attributes() should be @staticmethod
but not in this stupid and simple example.

Getting Attributes of a Class

19 Answers

Instance attributes only

Instance and class attributes

Must Read

Example

Robert Thorne