Question

I am having problems passing a method in a function. I have already looked at this previous post.

How do I pass a method as a parameter in Python

Here is a simple example of what I tried.

def passMethod(obj, method):
    return obj.method()

passMethod('Hi', lower)

In the end I will use this to help write a function dealing with GIS (Geographic Information Systems) data. The data is like an array. I want to add a new column NAME1 to the array. The array then has a method to call the column array.NAME1.

Regards,
Alex

Answer 1

When you give the name lower, that means to look up the name lower in the global namespace. It isn’t there, because you’re looking for the lower method of strings (the str class). That is spelled str.lower.

Then, in your function, obj.method means to look up the method attribute of the obj. It has nothing to do with the parameter named method, and cannot work that way. Instead, since you have an unbound method, pass the object as the self parameter explicitly: thus, method(obj). That gives us:

def passMethod(obj, method):
    return method(obj)

passMethod('Hi', str.lower)

Alternately, we could use a string as the name of the method to look up on the passed-in object. That looks like:

def passMethod(obj, method):
    return getattr(obj, method)()

passMethod('Hi', 'lower')