How to get a complete list of object's methods and attributes?

Question

dir(re.compile(pattern))

does not return pattern as one of the lists’s elements. Namely it returns:

['__copy__', '__deepcopy__', 'findall', 'finditer', 'match', 'scanner', 'search', 'split', 'sub', 'subn']

According to the manual, it is supposed to contain

the object’s attributes’ names, the
names of its class’s attributes, and
recursively of the attributes of its
class’s base classes.

It says also that

The list is not necessarily complete.

Is there a way to get the complete list? I always assumed that dir returns a complete list but apparently it does not…

Also: is there a way to list only attributes? Or only methods?

Edit: this is actually a bug in python -> supposedly it is fixed in the 3.0 branch (and perhaps also in 2.6)

Asked By: Bartosz Radaczyński

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Source

Answer 1

For the complete list of attributes, the short answer is: no. The problem is that the attributes are actually defined as the arguments accepted by the getattr built-in function. As the user can reimplement __getattr__, suddenly allowing any kind of attribute, there is no possible generic way to generate that list. The dir function returns the keys in the __dict__ attribute, i.e. all the attributes accessible if the __getattr__ method is not reimplemented.

For the second question, it does not really make sense. Actually, methods are callable attributes, nothing more. You could though filter callable attributes, and, using the inspect module determine the class methods, methods or functions.

Answered By: PierreBdR

Answer 2

That is why the new __dir__() method has been added in python 2.6

see:

http://docs.python.org/whatsnew/2.6.html#other-language-changes (scroll down a little bit)
http://bugs.python.org/issue1591665

Answered By: Moe

Answer 3

Here is a practical addition to the answers of PierreBdR and Moe:

For Python >= 2.6 and new-style classes, dir() seems to be enough.

For old-style classes, we can at least do what a standard module does to support tab completion: in addition to dir(), look for __class__, and then to go for its __bases__:

# code borrowed from the rlcompleter module
# tested under Python 2.6 ( sys.version = '2.6.5 (r265:79063, Apr 16 2010, 13:09:56) n[GCC 4.4.3]' )

# or: from rlcompleter import get_class_members
def get_class_members(klass):
    ret = dir(klass)
    if hasattr(klass,'__bases__'):
        for base in klass.__bases__:
            ret = ret + get_class_members(base)
    return ret


def uniq( seq ): 
    """ the 'set()' way ( use dict when there's no set ) """
    return list(set(seq))


def get_object_attrs( obj ):
    # code borrowed from the rlcompleter module ( see the code for Completer::attr_matches() )
    ret = dir( obj )
    ## if "__builtins__" in ret:
    ##    ret.remove("__builtins__")

    if hasattr( obj, '__class__'):
        ret.append('__class__')
        ret.extend( get_class_members(obj.__class__) )

        ret = uniq( ret )

    return ret

(Test code and output are deleted for brevity, but basically for new-style objects we seem to have the same results for get_object_attrs() as for dir(), and for old-style classes the main addition to the dir() output seem to be the __class__ attribute.)

Answered By: ジョージ

Answer 4

This is how I do it, useful for simple custom objects to which you keep adding attributes:

Given an object created with obj = type("Obj",(object,),{}), or by simply:

class Obj: pass
obj = Obj()

Add some attributes:

obj.name = 'gary'
obj.age = 32

then, to obtain a dictionary with only the custom attributes:

{key: value for key, value in obj.__dict__.items() if not key.startswith("__")}

# {'name': 'gary', 'age': 32}

Answered By: mluc

Answer 5

Only to supplement:

dir() is the most powerful/fundamental tool. (Most recommended)
Solutions other than dir() merely provide their way of dealing the output of dir().

Listing 2nd level attributes or not, it is important to do the sifting by yourself, because sometimes you may want to sift out internal vars with leading underscores __, but sometimes you may well need the __doc__ doc-string.
__dir__() and dir() returns identical content.
__dict__ and dir() are different. __dict__ returns incomplete content.
IMPORTANT: __dir__() can be sometimes overwritten with a function, value or type, by the author for whatever purpose.

Here is an example:
```
\...\torchfun.py in traverse(self, mod, search_attributes)
445             if prefix in traversed_mod_names:
446                 continue
447             names = dir(m)
448             for name in names:
449                 obj = getattr(m,name)
```
TypeError: descriptor __dir__ of 'object' object needs an argument

The author of PyTorch modified the __dir__() method to something that requires an argument. This modification makes dir() fail.
If you want a reliable scheme to traverse all attributes of an object, do remember that every pythonic standard can be overridden and may not hold, and every convention may be unreliable.

Answered By: Chiron

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