[Python-Dev] Issue10403 - using 'attributes' instead of members in documentation (original) (raw)

Terry Reedy tjreedy at udel.edu
Tue Jun 28 18:12:24 CEST 2011

On 6/28/2011 9:20 AM, Steven D'Aprano wrote:

>>> class C: ... def method(self, x): ... return x+1 ... >>> c = C() >>> c.method = types.MethodType(lambda self, x: x+101, c)

types.MethodType creates a bound method, not a method. A bound method is a partial or curried function, which is to say, a function.

Herw and below, I am ignoring the fact that the example ignores self. My comments would be the same for "lambda self,x: return self.value+x"

>>> c.method(1)

The fact that you make the bound function an attribute of the same object to which it is bound is irrelevant to how it acts when called. It only affect how you access it. You could bind it to anything else, including another instance or a plain name:

d = C() d.method = types.MethodType(lambda self, x: x+101, c) d.method(1)

m = types.MethodType(lambda self, x: x+101, c) m(1)

102

I don't know how rare it is, but it's a useful trick for customising the behaviour of instances.

As I see it, there are three dichotomies we sometimes need to make: (1) Instance attributes vs class (shared) attributes. (2) Computed vs non-computed attributes. (3) Method attributes (methods) vs non-method/data attributes.

Nicely put so far...

The three are orthogonal:

Non-class instance function attributes are not methods in any useful sense.

a staticmethod is a method by virtue of being callable

A 'staticmethod' is a non-method class function attribute. The name is unfortunate. 'Static' mean 'does not get the dynamic method treatment'.

Strictly speaking, (3) is not truly a dichotomy,

I disagree here. A method is usefully defined as a class function attribute that gets an automagic first arg when accessed and called 'normally'. In other words, the dichotomy is needed because being a method affects the meaning of syntax.

since functions and methods are first class-objects in Python. E.g. one may store a function as an attribute with the intention of using it as data rather than as a method.

The fact that one can also access a method as a function does not negate the effect on syntax.

"methods are things you call"

Way too broad, even for attributes. Callable things are methods when 'a.b(c)' causes a to be the first arg of b.

-- Terry Jan Reedy

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