Is there a built-in function to print all the current properties and values of an object?

Question

So what I'm looking for here is something like PHP's print_r function.

This is so I can debug my scripts by seeing what's the state of the object in question.

Solution 1

You want vars() mixed with pprint():

from pprint import pprint
pprint(vars(your_object))

Solution 2

def dump(obj):
  for attr in dir(obj):
    print("obj.%s = %r" % (attr, getattr(obj, attr)))

There are many 3rd-party functions out there that add things like exception handling, national/special character printing, recursing into nested objects etc. according to their authors' preferences. But they all basically boil down to this.

Solution 3

dir has been mentioned, but that'll only give you the attributes' names. If you want their values as well try __dict__.

class O:
   def __init__ (self):
      self.value = 3

o = O()

Here is the output:

>>> o.__dict__

{'value': 3}

Solution 4

Is there a built-in function to print all the current properties and values of an object?

No. The most upvoted answer excludes some kinds of attributes, and the accepted answer shows how to get all attributes, including methods and parts of the non-public api. But there is no good complete builtin function for this.

So the short corollary is that you can write your own, but it will calculate properties and other calculated data-descriptors that are part of the public API, and you might not want that:

from pprint import pprint
from inspect import getmembers
from types import FunctionType

def attributes(obj):
    disallowed_names = {
      name for name, value in getmembers(type(obj)) 
        if isinstance(value, FunctionType)}
    return {
      name: getattr(obj, name) for name in dir(obj) 
        if name[0] != '_' and name not in disallowed_names and hasattr(obj, name)}

def print_attributes(obj):
    pprint(attributes(obj))

Problems with other answers

Observe the application of the currently top voted answer on a class with a lot of different kinds of data members:

from pprint import pprint

class Obj:
    __slots__ = 'foo', 'bar', '__dict__'
    def __init__(self, baz):
        self.foo = ''
        self.bar = 0
        self.baz = baz
    @property
    def quux(self):
        return self.foo * self.bar

obj = Obj('baz')
pprint(vars(obj))

only prints:

{'baz': 'baz'}

Because vars only returns the __dict__ of an object, and it's not a copy, so if you modify the dict returned by vars, you're also modifying the __dict__ of the object itself.

vars(obj)['quux'] = 'WHAT?!'
vars(obj)

returns:

{'baz': 'baz', 'quux': 'WHAT?!'}

-- which is bad because quux is a property that we shouldn't be setting and shouldn't be in the namespace...

Applying the advice in the currently accepted answer (and others) is not much better:

>>> dir(obj)
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__slots__', '__str__', '__subclasshook__', 'bar', 'baz', 'foo', 'quux']

As we can see, dir only returns all (actually just most) of the names associated with an object.

inspect.getmembers, mentioned in the comments, is similarly flawed - it returns all names and values.

From class

When teaching I have my students create a function that provides the semantically public API of an object:

def api(obj):
    return [name for name in dir(obj) if name[0] != '_']

We can extend this to provide a copy of the semantic namespace of an object, but we need to exclude __slots__ that aren't assigned, and if we're taking the request for "current properties" seriously, we need to exclude calculated properties (as they could become expensive, and could be interpreted as not "current"):

from types import FunctionType
from inspect import getmembers

def attrs(obj):
    disallowed_properties = {
        name for name, value in getmembers(type(obj)) 
        if isinstance(value, (property, FunctionType))
    }
    return {
        name: getattr(obj, name) for name in api(obj) 
        if name not in disallowed_properties and hasattr(obj, name)
    }

And now we do not calculate or show the property, quux:

>>> attrs(obj)
{'bar': 0, 'baz': 'baz', 'foo': ''}

Caveats

But perhaps we do know our properties aren't expensive. We may want to alter the logic to include them as well. And perhaps we want to exclude other custom data descriptors instead.

Then we need to further customize this function. And so it makes sense that we cannot have a built-in function that magically knows exactly what we want and provides it. This is functionality we need to create ourselves.

Conclusion

There is no built-in function that does this, and you should do what is most semantically appropriate for your situation.

Solution 5

You can use the "dir()" function to do this.

>>> import sys
>>> dir(sys)
['__displayhook__', '__doc__', '__excepthook__', '__name__', '__stderr__', '__stdin__', '__stdo
t__', '_current_frames', '_getframe', 'api_version', 'argv', 'builtin_module_names', 'byteorder
, 'call_tracing', 'callstats', 'copyright', 'displayhook', 'dllhandle', 'exc_clear', 'exc_info'
 'exc_type', 'excepthook', 'exec_prefix', 'executable', 'exit', 'getcheckinterval', 'getdefault
ncoding', 'getfilesystemencoding', 'getrecursionlimit', 'getrefcount', 'getwindowsversion', 'he
version', 'maxint', 'maxunicode', 'meta_path', 'modules', 'path', 'path_hooks', 'path_importer_
ache', 'platform', 'prefix', 'ps1', 'ps2', 'setcheckinterval', 'setprofile', 'setrecursionlimit
, 'settrace', 'stderr', 'stdin', 'stdout', 'subversion', 'version', 'version_info', 'warnoption
', 'winver']
>>>

Another useful feature is help.

>>> help(sys)
Help on built-in module sys:

NAME
    sys

FILE
    (built-in)

MODULE DOCS
    http://www.python.org/doc/current/lib/module-sys.html

DESCRIPTION
    This module provides access to some objects used or maintained by the
    interpreter and to functions that interact strongly with the interpreter.

    Dynamic objects:

    argv -- command line arguments; argv[0] is the script pathname if known

View more solutions

Comments

[Admin]

unpythonic, because follows not-invented-here

[Dan Lenski]

Say what? Sure, you can use the getmembers() function in the standard inspect module, but I thought this would be more useful in that it illustrates how to do introspection in general.

[Admin]

even then it sets a bad example, because you essentially reemplemented obj.__dict__ .

[Dan Lenski]

NOT AT ALL. dir(obj) shows properties that aren't found in __dict__ (such as __doc__ and __module__). Furthermore, __dict__ doesn't work at all for objects declared with __slots__. In general, __dict__ shows user-level properties that are actually stored in a dictionary internally. dir() shows more.

[Admin]

what are you talking about? both __module__ and __doc__ are in __dict__!

[Admin]

vars() simply returns the __dict__ of its argument and that is also the fallback of dir() in case there is no __dir__ method. so use dir() in the first place, as i said.

[hobs]

Some classes/objects don't contain any __dict__ attribute/member. I know it's crazy, but true. Built-ins like int and str or re.MatchObjects are common examples. Try 'hello'.__dict__, then try dir('hello')

[Timmmm]

@hop: dir() gives you all the built in things you probably don't care about like __str__ and __new__. var() doesn't.

[sdaau]

Well, this answer at least prints both attributes' names and values, in case an object doesn't have a dict (like the return from, say, QtGui.QMdiSubWindow.sizePolicy()), which is what I like about it.

[port5432]

I like the vars/pprint option above, but this is good as it does not require inclusion of an libraries.

[Raz]

Shouldn't that be for key,value in obj.__dict__.iteritems(): print key,value?

[Tim Ogilvy]

this didn't work on python 3. Had to install pymongo and do it as per @Clark 's answer

[Tim Ogilvy]

Okay yep had to install pymongo tho to use it.

[phobie]

This should be a pip and a deb not only a gist!

[anatoly techtonik]

This fails on sets and other objects that doesn't have __dict__ attribute.

[anatoly techtonik]

Objects like set doesn't have __dict__, so for them it will fail with AttributeError: 'set' object has no attribute '__dict__'

[AlejandroVD]

This option is useful for printing strings concatenated with the content of the object: print "DEBUG: object value: " + repr(obj)

[memeplex]

> So in a nutshell, python is all about this great object oriented paradigm, but the tools you get out of the box are designed for working with something other than objects... Quite a claim when the only example you're providing is a module of secondary importance.

[Jordan]

LOL Tenable use this in their Nessus python library (see the objdump function) github.com/tenable/nessrest/blob/…

[Dan Lenski]

Indeed… verbatim! Wow :-D github.com/tenable/nessrest/blob/…

[AlxVallejo]

>with some custom classes ... This is why I'm not a fan of python. Things "sometimes" work and "sometimes" not

[hidefromkgb]

I do not care whether that`s «unpythonic» or whatnot. It gets the job done, which in debugging is the one and only thing that matters.

[Fernando César]

Used your explanation on inspect to improve the most complete answer. Hope that's ok with you.

[Peter Wood]

@memeplex where does it say python is all about OOP?

[memeplex]

Ok, it just says it's all about this great OOP, my bad.

[Wavesailor]

This module does not seemed to be maintained any more and have a number of open issues. Rather use ppretty

[rob]

as with many of the other answers here TypeError: vars() argument must have __dict__ attribute

[rob]

get no errors, but not recursive so just get a lot of hex addresses

[Joseph Astrahan]

exactly what I was looking for for quick debug :), great find!

[Joseph Astrahan]

little hint add depth=6 (or however far you need) as one of the parameters for it and the recursion details can go further :). One of the things I like about how it prints lists is it shows the first 2 entires and last 2 entries so you know it's working

[Rainb]

this is only for 2.7

[Basil Musa]

The best answer so far. To hell with "unpythonic" approaches : )))

[joe-khoa]

this is absolutely good anwers, adding more: from inspect import getmembers

[cowlinator]

@hop, vars() gives the values of the fields, while dir() leaves them a mystery.

[Sion C]

str(pformat(vars(session)).encode('utf-8')).replace('\\n', '\n').replace('\\t', '\t') - dont kill me but with utf8 that what works

[NZD]

pypi.org/project/beeprint (or github.com/panyanyany/beeprint) pretty prints 'everything' and also recursively.

[Smart Manoj]

that what for parameters to get customized thing from a function

[Smart Manoj]

@NZD not works for from collections import * ; obj=Counter([3,4])

[Vladimir]

Addition to exclude all built-in vars (methods, functions etc) : {attr: getattr(your_obj, attr) for attr in dir(your_obj) and "__" not in attr}

[ejkitchen]

This is the most comprehensive answer and should be upvoted more

[TCSGrad]

Holy eff, THIS is the answer i was looking for. Why it isnt the accepted answer, i'll never know.

[Admin]

Nice, suited. But fixed compile errors (maybe, other Python version) for key, value in params.__dict__.items(): print(key + " = " + str(value))