Call a method of an object with arguments in Python

Question

I want to be able to call different methods on a Python class with dynamic function name, e.g.

class Obj(object):
    def A(self, x):
        print "A %s" % x

    def B(self, x):
        print "B %s" % x

o = Obj()

 # normal route
o.A(1) # A 1
o.B(1) # B 1

 # dynamically
foo(o, "A", 1) # A 1; equiv. to o.A(1)
foo(o, "B", 1) # B 1

What is "foo"? (or is there some other approach?) I'm sure it must exist, but I just can't seem to find it or remember what it is called. I've looked at getattr, apply, and others in the list of built-in functions. It's such a simple reference question, but alas, here I am!

Thanks for reading!

Sven Marnach · Accepted Answer · 2011-03-30 15:08:17Z

46

Well, getattr indeed seems to be what you want:

getattr(o, "A")(1)

is equivalent to

o.A(1)

answered Mar 30, 2011 at 15:08

Sven Marnach

608k123 gold badges966 silver badges865 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

RPDeshaies Over a year ago

Is there a way to do the same thing but from a class name instead of a method name ? E.g. getClass("MyClassName") and than use the getattr() method on this object to get a method inside it ?

Sven Marnach Over a year ago

@Tareck117: You can use globals()["MyClass"] to look up a name in the global scope of the current module, or getattr(some_module, "MyClass") if it's in a different module. That said, in most (~99%) of the cases I've seen people using class or variables names as data, they had an issue with their design.

RPDeshaies Over a year ago

Thanks @Sven, I guess this will help me but since you think I may have a design problem I'll explain myself (I'm coming from a ASP/C# perspective): I would like to call a Python Web Service (CheeryPy) via some $.ajax call in javascript by passing the name of the controller to execute and the name of the method to call in the controller to create some sort of router. Do you know a cleaner way of doing this ?

RPDeshaies Over a year ago

Also, is it a bad pratice to call a method from a string argument using the getattr(o, "A")(1) call ?

Sven Marnach Over a year ago

@Tareck117: It's hard to know without the context. There are valid uses for globals(), and there are valid uses for getattr(), but both are also abused often. My feeling is that most uses of globals() are questionable. Never use getattr() with a string literal as second argument -- use normal argument access in that case.

Ignacio Vazquez-Abrams · Accepted Answer · 2011-03-30 15:08:29Z

9

Methods in Python are first-class objects.

getattr(o, 'A')(1)

answered Mar 30, 2011 at 15:08

Ignacio Vazquez-Abrams

804k160 gold badges1.4k silver badges1.4k bronze badges

Collectives™ on Stack Overflow

Call a method of an object with arguments in Python

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related