Shortest way of creating an object with arbitrary attributes in Python?

Question

Hey, I just started wondering about this as I came upon a code that expected an object with a certain set of attributes (but with no specification of what type this object should be).

One solution would be to create a new class that has the attributes the code expects, but as I call other code that also needs objects with (other) attributes, I'd have to create more and more classes.

A shorter solution is to create a generic class, and then set the attributes on instances of it (for those who thought of using an instance of object instead of creating a new class, that won't work since object instances don't allow new attributes).

The last, shortest solution I came up with was to create a class with a constructor that takes keyword arguments, just like the dict constructor, and then sets them as attributes:

class data:
    def __init__(self, **kw):
        for name in kw:
            setattr(self, name, kw[name])

options = data(do_good_stuff=True, do_bad_stuff=False)

But I can't help feeling like I've missed something obvious... Isn't there a built-in way to do this (preferably supported in Python 2.5)?

Answer 1

type('', (), {})() will create an object that can have arbitrary attributes.

Example:

obj = type('', (), {})()
obj.hello = "hello"
obj.world = "world"
print obj.hello, obj.world   # will print "hello world"

type() with three arguments creates a new type.

• The first argument '' is the name of the new type. We don't care about the name, so we leave it empty.

• The second argument () is a tuple of base types. Here object is implicit.

• The third argument is a dictionary of attributes of the new object. We start off with no attributes so it's empty {} .

In the end we instantiate a new instance of this new type with () .

Answer 2

The original code can be streamlined a little by using __dict__ :

In [1]: class data:
   ...:     def __init__(self, **kwargs):
   ...:         self.__dict__.update(kwargs)
   ...: 

In [2]: d = data(foo=1, bar=2)

In [3]: d.foo
Out[3]: 1

In [4]: d.bar
Out[4]: 2

In Python 3.3 and greater, this syntax is made available by the types.SimpleNamespace class.

Answer 3

Use collections.namedtuple .

It works well.

from collections import namedtuple
Data = namedtuple( 'Data', [ 'do_good_stuff', 'do_bad_stuff' ] )
options = Data( True, False )

Answer 4

This is the shortest way I know

>>> obj = type("myobj",(object,),dict(foo=1,bar=2))
>>> obj.foo
1
>>> obj.bar
2
>>> 

using dict instead of {} insures your attribute names are valid

>>> obj = type("myobj",(object,),{"foo-attr":1,"bar-attr":2})
>>> obj.foo-attr
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'myobj' has no attribute 'foo'
>>>

Answer 5

This works in 2.5, 2.6, and 3.1:

class Struct(object):
    pass

something = Struct()
something.awesome = abs

result = something.awesome(-42)

EDIT: I thought maybe giving the source would help out as well. http://docs.python.org/tutorial/classes.html#odds-and-ends

EDIT: Added assignment to result, as I was using the interactive interpreters to verify, and you might not be.

Answer 6

A function is an object. So you could assign attributes to a function. Or make one. This is the simplest way in terms of lines of code, I think.

def hello():
    pass


hello.chook = 123

but the easiest and most elegant way (but Python 3.3+) is to use the standard libary's SimpleNamespace :

>>> from types import SimpleNamespace
>>> foo = SimpleNamespace()
>>> foo.hello = "world"

Answer 7

Use a combination between lambda and type build-in, I think is the smallest way to do that:

obj = lambda **kwargs: type('obj', (object,), kwargs)()

options = obj(do_good_stuff=True, do_bad_stuff=False)

print options.do_good_stuff
print options.do_bad_stuff

Answer 8

If you don't need to pass values in the constructor, you can do this:

class data: pass

data.foo = 1
data.bar = 2

You use the class static member variables to hold your data.

Answer 9

If I understand your question correctly, you need records. Python classes may be used this way, which is what you do.

I believe the most pythonic way of dealing with "records" is simply... dictionaries ! A class is a sort of dictionary on steroids.

Your class example data is essentially a way of converting a dictionary into a class.

(On a side note, I would rather use self.__setattr__(name, kw[name]) .)

Answer 10

You might be interested in the "Struct", which is part of the IPython package. It does what you want to do, with lots of useful methods.

http://ipython.org/ipython-doc/rel-0.13/api/generated/IPython.utils.ipstruct.html

Answer 11

这通常是您会使用 dict 的东西，而不是创建一个类。