looping over all member variables of a class in python

100
votes

How do you get a list of all variables in a class thats iteratable? Kind of like locals(), but for a class

class Example(object):
    bool143 = True
    bool2 = True
    blah = False
    foo = True
    foobar2000 = False

    def as_list(self)
       ret = []
       for field in XXX:
           if getattr(self, field):
               ret.append(field)
       return ",".join(ret)

this should return

>>> e = Example()
>>> e.as_list()
bool143, bool2, foo
8
python
Why can't use use for field in [ self.bool143, self.bool2, self.blah, self.foo, self.foobar2000 ]? How does it happen that you don't know the instance variables of the class? – S.Lott
S.Lott: thats what I ended up doing anyways. In my real code, I have like 40 variables, and I thought it'd be better and more DRY to not have to manually make the iteration list. – priestc
Possible duplicate of Iterate over object attributes in python – Trevor Boyd Smith
Related: python - Is there a built-in function to print all the current properties and values of an object? - Stack Overflow – user202729

8 Answers

170
votes
dir(obj)

gives you all attributes of the object. You need to filter out the members from methods etc yourself:

class Example(object):
    bool143 = True
    bool2 = True
    blah = False
    foo = True
    foobar2000 = False

example = Example()
members = [attr for attr in dir(example) if not callable(getattr(example, attr)) and not attr.startswith("__")]
print members

Will give you:

['blah', 'bool143', 'bool2', 'foo', 'foobar2000']
132
votes

If you want only the variables (without functions) use:

vars(your_object)
31
votes

@truppo: your answer is almost correct, but callable will always return false since you're just passing in a string. You need something like the following:

[attr for attr in dir(obj()) if not callable(getattr(obj(),attr)) and not attr.startswith("__")]

which will filter out functions

6
votes
>>> a = Example()
>>> dir(a)
['__class__', '__delattr__', '__doc__', '__format__', '__getattribute__', '__hash__',
'__init__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__',
'__sizeof__', '__str__', '__subclasshook__', 'bool143', 'bool2', 'blah',
'foo', 'foobar2000', 'as_list']

—as you see, that gives you all attributes, so you'll have to filter out a little bit. But basically, dir() is what you're looking for.

0
votes

Similar to vars(), one can use the below code to list all class attributes. It is equivalent to vars(example).keys().

example.__dict__.keys()
-1
votes
row2dict = lambda r: {c.name: str(getattr(r, c.name)) for c in r.__table__.columns} if r else {}

Use this.

-2
votes
    class Employee:
    '''
    This class creates class employee with three attributes 
    and one function or method
    '''

    def __init__(self, first, last, salary):
        self.first = first
        self.last = last
        self.salary = salary

    def fullname(self):
        fullname=self.first + ' ' + self.last
        return fullname

emp1 = Employee('Abhijeet', 'Pandey', 20000)
emp2 = Employee('John', 'Smith', 50000)

print('To get attributes of an instance', set(dir(emp1))-set(dir(Employee))) # you can now loop over
-4
votes

The easy way to do this is to save all instances of the class in a list.

a = Example()
b = Example()
all_examples = [ a, b ]

Objects don't spring into existence spontaneously. Some part of your program created them for a reason. The creation is done for a reason. Collecting them in a list can also be done for a reason.

If you use a factory, you can do this.

class ExampleFactory( object ):
    def __init__( self ):
        self.all_examples= []
    def __call__( self, *args, **kw ):
        e = Example( *args, **kw )
        self.all_examples.append( e )
        return e
    def all( self ):
        return all_examples

makeExample= ExampleFactory()
a = makeExample()
b = makeExample()
for i in makeExample.all():
    print i