Python dictionary from an object's fields

Question

Do you know if there is a built-in function to build a dictionary from an arbitrary object? I'd like to do something like this:

>>> class Foo:
...     bar = 'hello'
...     baz = 'world'
...
>>> f = Foo()
>>> props(f)
{ 'bar' : 'hello', 'baz' : 'world' }

NOTE: It should not include methods. Only fields.

Thanks

Answer 1

The dir builtin will give you all the object's attributes, including special methods like __str__, __dict__ and a whole bunch of others which you probably don't want. But you can do something like:

>>> class Foo(object):
...     bar = 'hello'
...     baz = 'world'
...
>>> f = Foo()
>>> [name for name in dir(f) if not name.startswith('__')]
[ 'bar', 'baz' ]
>>> dict((name, getattr(f, name)) for name in dir(f) if not name.startswith('__')) 
{ 'bar': 'hello', 'baz': 'world' }

So can extend this to only return data attributes and not methods, by defining your props function like this:

import inspect

def props(obj):
    pr = {}
    for name in dir(obj):
        value = getattr(obj, name)
        if not.name.startswith('__') and not inspect.ismethod(value):
            pr[name] = value
    return pr

Answer 2

Is there a way to exclude methods from the solution posted above?

Answer 3

I've settled with a combination of both answers:

dict((key, value) for key, value in f.__dict__.iteritems() 
    if not callable(value) and not key.startswith('__'))

Answer 4

The "if not callable(...)" filter does exclude methods.

Answer 5

Note that best practice in current versions of Python is to use new-style classes, i.e.

class Foo(object):
    ...

Also, there's a difference between an 'object' and a 'class'. To build a dictionary from an arbitrary object, it's sufficient to use __dict__. Usually, you'll declare your methods at class level and your attributes at instance level, so __dict__ should be fine. For example:

>>> class A(object):
...   def __init__(self):
...     self.b = 1
...     self.c = 2
...   def do_nothing(self):
...     pass
...
>>> a = A()
>>> a.__dict__
{'c': 2, 'b': 1}

Alternatively, depending on what you want to do, it might be nice to inherit from dict. Then your class is already a dictionary, and if you want you can override getattr and/or setattr to call through and set the dict. For example:

class Foo(dict):
    def __init__(self):
        pass
    def __getattr__(self, attr):
        return self[attr]

    # etc...

Answer 6

To build a dictionary from an arbitrary object, it's sufficient to use dict.

This misses attributes that the object inherits from its class. For example,

class c(object):
    x = 3
a = c()

hasattr(a, 'x') is true, but 'x' does not appear in a.__dict__