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.
Note that best practice in Python 2.7 is to use new-style classes (not needed with Python 3), 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}
A better approach (suggested by robert in comments) is the builtin vars function:
>>> vars(a)
{'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...
Instead of x.__dict__, it's actually more pythonic to use vars(x).
MyClass(**my_dict), assuming you have defined a constructor with parameters that mirror the class attributes. No need to access private attributes or override dict. - tvt173
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
ismethod doesn't catch functions. Example: inspect.ismethod(str.upper). inspect.isfunction isn't much more helpful, though. Not sure how to approach this right away. - Ehtesh Choudhury
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('__'))
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__
I thought I'd take some time to show you how you can translate an object to dict via dict(obj).
class A(object):
d = '4'
e = '5'
f = '6'
def __init__(self):
self.a = '1'
self.b = '2'
self.c = '3'
def __iter__(self):
# first start by grabbing the Class items
iters = dict((x,y) for x,y in A.__dict__.items() if x[:2] != '__')
# then update the class items with the instance items
iters.update(self.__dict__)
# now 'yield' through the items
for x,y in iters.items():
yield x,y
a = A()
print(dict(a))
# prints "{'a': '1', 'c': '3', 'b': '2', 'e': '5', 'd': '4', 'f': '6'}"
The key section of this code is the __iter__ function.
As the comments explain, the first thing we do is grab the Class items and prevent anything that starts with '__'.
Once you've created that dict, then you can use the update dict function and pass in the instance __dict__.
These will give you a complete class+instance dictionary of members. Now all that's left is to iterate over them and yield the returns.
Also, if you plan on using this a lot, you can create an @iterable class decorator.
def iterable(cls):
def iterfn(self):
iters = dict((x,y) for x,y in cls.__dict__.items() if x[:2] != '__')
iters.update(self.__dict__)
for x,y in iters.items():
yield x,y
cls.__iter__ = iterfn
return cls
@iterable
class B(object):
d = 'd'
e = 'e'
f = 'f'
def __init__(self):
self.a = 'a'
self.b = 'b'
self.c = 'c'
b = B()
print(dict(b))
Late answer but provided for completeness and the benefit of googlers:
def props(x):
return dict((key, getattr(x, key)) for key in dir(x) if key not in dir(x.__class__))
This will not show methods defined in the class, but it will still show fields including those assigned to lambdas or those which start with a double underscore.
If you want to list part of your attributes, override __dict__:
def __dict__(self):
d = {
'attr_1' : self.attr_1,
...
}
return d
# Call __dict__
d = instance.__dict__()
This helps a lot if your instance get some large block data and you want to push d to Redis like message queue.
I think the easiest way is to create a getitem attribute for the class. If you need to write to the object, you can create a custom setattr . Here is an example for getitem:
class A(object):
def __init__(self):
self.b = 1
self.c = 2
def __getitem__(self, item):
return self.__dict__[item]
# Usage:
a = A()
a.__getitem__('b') # Outputs 1
a.__dict__ # Outputs {'c': 2, 'b': 1}
vars(a) # Outputs {'c': 2, 'b': 1}
dict generates the objects attributes into a dictionary and the dictionary object can be used to get the item you need.
__dict__ - radtek
A downside of using __dict__ is that it is shallow; it won't convert any subclasses to dictionaries.
If you're using Python3.5 or higher, you can use jsons:
>>> import jsons
>>> jsons.dump(f)
{'bar': 'hello', 'baz': 'world'}
class DateTimeDecoder(json.JSONDecoder):
def __init__(self, *args, **kargs):
JSONDecoder.__init__(self, object_hook=self.dict_to_object,
*args, **kargs)
def dict_to_object(self, d):
if '__type__' not in d:
return d
type = d.pop('__type__')
try:
dateobj = datetime(**d)
return dateobj
except:
d['__type__'] = type
return d
def json_default_format(value):
try:
if isinstance(value, datetime):
return {
'__type__': 'datetime',
'year': value.year,
'month': value.month,
'day': value.day,
'hour': value.hour,
'minute': value.minute,
'second': value.second,
'microsecond': value.microsecond,
}
if isinstance(value, decimal.Decimal):
return float(value)
if isinstance(value, Enum):
return value.name
else:
return vars(value)
except Exception as e:
raise ValueError
Now you can use above code inside your own class :
class Foo():
def toJSON(self):
return json.loads(
json.dumps(self, sort_keys=True, indent=4, separators=(',', ': '), default=json_default_format), cls=DateTimeDecoder)
Foo().toJSON()
__dict__won't work if the object is using slots (or defined in a C module). - Antimonyvars(a)do this? For me it's preferable to invoking the__dict__directly. - robert__getattr__ = dict.__getitem__to exactly replicate the behaviour, then you would also want__setattr__ = dict.__setitem__and__delattr__ = dict.__delitem__for complete-ness. - Tadhg McDonald-Jensen