On 26Dec2018 01:06, Alan Gauld <alan.ga...@yahoo.co.uk> wrote:
On 26/12/2018 00:00, Avi Gross wrote:
great. Many things in python can be made to fit and some need work.
Dumb example is that sorting something internally returns None and
not the object itself.
This is one of my few complaints about Python.
In Smalltalk the default return value from
any method is self. In Python it is None.
self allows chaining of methods, None does not.
[...]
Smalltalk uses this technique so much it has
its own code layout idiom (Pythonised as
follows):
object
.method1()
.method2()
.method3()
....
.lastone()
While I see your point, the Python distinction is that methods returning
values tend to return _independent_ values; the original object is not
normally semanticly changed. As you know.
To take the builtin sorted() example, let us soppose object is a
collection, such as a list. I would not want:
object.sort()
to return the list because that method has a side effect on object.
By contract, I'd be happy with a:
object.sorted()
method returning a new list because it hasn't changes object, and it
returns a nice chaining capable object for continued use.
But that way lies a suite of doubled methods for most classes: one to
apply some operation to an object, modifying it, and its partner to
produce a new object (normally of the same type) being a copy of the
first object with the operation applied.
To me it is the side effect on the original object which weighs against
modification methods returning self.
Here's a shiny counter example for chaining.
thread1:
print(object.sorted())
thread2:
print(object.sorted(reverse=True))
The above employs composable methods. And they conflict. When methods
return a copy the above operation is, loosely speaking, safe:
thread1:
print(sorted(object))
thread2:
print(sorted(object,reverse=True))
Cheers,
Cameron Simpson <c...@cskk.id.au>
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
https://mail.python.org/mailman/listinfo/tutor
