How to access object attribute given string corresponding to name of that attribute

Question

How do you set/get the values of attributes of t given by x?

class Test:
   def __init__(self):
       self.attr1 = 1
       self.a         


        

Answer 1

Note: This answer is very outdated. It applies to Python 2 using the new module that was deprecated in 2008.

There is python built in functions setattr and getattr. Which can used to set and get the attribute of an class.

A brief example:

>>> from new import  classobj

>>> obj = classobj('Test', (object,), {'attr1': int, 'attr2': int}) # Just created a class

>>> setattr(obj, 'attr1', 10)

>>> setattr(obj, 'attr2', 20)

>>> getattr(obj, 'attr1')
10

>>> getattr(obj, 'attr2')
20

Answer 2

If you want to keep the logic hidden inside the class, you may prefer to use a generalized getter method like so:

class Test:
    def __init__(self):
        self.attr1 = 1
        self.attr2 = 2

    def get(self,varname):
        return getattr(self,varname)

t = Test()
x = "attr1"
print ("Attribute value of {0} is {1}".format(x, t.get(x)))

Outputs:

Attribute value of attr1 is 1

Another apporach that could hide it even better would be using the magic method __getattribute__, but I kept getting an endless loop which I was unable to resolve when trying to get retrieve the attribute value inside that method.

Also note that you can alternatively use vars(). In the above example, you could exchange getattr(self,varname) by return vars(self)[varname], but getattrmight be preferable according to the answer to What is the difference between vars and setattr?.

Answer 3

There are built-in functions called getattr and setattr

getattr(object, attrname)
setattr(object, attrname, value)

In this case

x = getattr(t, 'attr1')
setattr(t, 'attr1', 21)