[ACCEPTED]-Assigning a function to an object attribute-methods

Accepted answer

Score: 18

Here is how you do it:

import types
class Scriptable:
    def __init__(self, script = None):
        if script is not None:
            self.script = types.MethodType(script, self)   # replace the method
    def script(self):
        print("greetings from the default script")

As ba__friend noted 7 in the comments, methods are stored on the 6 class object. A descriptor on the class object 5 returns functions as bound methods when 4 you access the attribute from a instance.

When 3 you assign a function to a instance nothing happens 2 special happens, so you have to wrap the 1 function yourself.

Score: 11

Thanks to Alex Martelli's answer here is another 1 version:

class Scriptable:
    def script(self):
        print(self)
        print("greetings from the default script")

def another_script(self):
    print(self)
    print("greetings from the another script")

s = Scriptable()
s.script()

# monkey patching:
s.script = another_script.__get__(s, Scriptable)
s.script()

Score: 7

Look at this:

>>> scriptable = Scriptable()
>>> scriptable.script
<bound method Scriptable.script of <__main__.Scriptable instance at 0x01209DA0>>
>>> scriptable = Scriptable(my_script)
>>> scriptable.script
<function my_script at 0x00CF9730>

Statement self.script = script creates only an 8 attribute of a class object, without any 7 'magic' with it.

Statement def script(self): inside a class 6 definition creates a descriptor - special 5 object that actually manages all stuff with 4 the self parameter.

You can read more about descriptors 3 in Python in the mentioned Data model reference: implementing-descriptors.

One 2 more great article about descriptors in 1 Python from Raymond Hettinger: How-To Guide for Descriptors.

Score: 1

I can't really answer your question why it 3 works like that, you'll have to ask Guido 2 van Rossum, but I can give you a possible 1 workaround:

class Scriptable:
    def __init__(self, script = None):
        self._script = script # replace the method
    def script(self):
        if self._script: return self._script(self)
        return self._defaultscript()
    def _defaultscript(self):
        print("greetings from the default script")

Source: stackoverflow.com

[ACCEPTED]-Assigning a function to an object attribute-methods

What are the parentheses for at the end of Python method names?

In Python, how can I find the index of the first item in a list that is NOT some value?

Call a function without waiting for it

Python Profiling: What does "method 'poll' of 'select.poll' objects"?

Easy way of overriding default methods in custom Python classes?

Differences between data attributes and method attributes

Why always add self as first argument to class methods?

How to test if a class attribute is an instance method

Check if a function is a method of some object

python: What happens when class attribute, instance attribute, and method all have the same name?