Comments on: No need for set/get methods in Python

By: amanita

amanita — Mon, 26 Jan 2009 13:38:27 +0000

Instead of
Book.title = ‘Code Complete’
shouldn’t write:
book = Book()
book.title = ‘Code Complete’

With:
book._title = ‘foo’
I can modify the property from the outside anyway … right?

By: Nisse

Nisse — Wed, 29 Oct 2008 11:20:55 +0000

Well, those both seem obsolete after seeing how it’s done in ruby.

class Book
attr_accessor :title
end

which gives you

book = Book.new
book.title = ‘rftw’
puts book.title # => “rftw”

By: Federico

Federico — Tue, 19 Aug 2008 13:43:50 +0000

Hi masklinn,

> Don’t use double underscore prefixes. Ever.
Changed. Thanks for the tip.

> with Python 2.4 or more recent, you can use the ‘property’ function
Nice :)

By: masklinn

masklinn — Tue, 19 Aug 2008 08:31:01 +0000

Another remark: with Python 2.4 or more recent, you can use the `property` function (because it’s nothing more) as a decorator if you want e.g. to create a read-only property or make a member read-only:

>>> class Foo(object):
….def __init__(self, some_value):
……..self.some_value = some_value

>>> foo = Foo(42)
>>> foo.some_value
42
>>> foo.some_value = 5
>>> foo.some_value
5
>>> class Foo(object):
….def __init__(self, some_value):
……..self._some_value = some_value
….@property
….def some_value(self):
……..return self._some_value

>>> foo = Foo(42)
>>> foo.some_value
42
>>> foo.some_value = 5

Traceback (most recent call last):
..File “”, line 1, in
….foo.some_value = 5
AttributeError: can’t set attribute
>>>

By: masklinn

masklinn — Tue, 19 Aug 2008 08:23:08 +0000

Remarks from a pythonista:

* Don’t use double underscore prefixes. Ever. It’s bad style. A single underscore is all you need, don’t go for more, name mangling wasn’t introduced to create pseudo-private members.

* While I realize it’s for the sake of the example, don’t create empty properties (the ones you’ve created here) either, they create indirection and make the code slower and more complex for no gain. You can transparently introduce properties later if and when you need them.

By: Robert

Robert — Mon, 18 Aug 2008 19:56:46 +0000

I use a technique using __call() instead of __get() and __set(). propertys are get and set using the convention used for functions like session_id(), where the function called with no args will return the current value, and the property can be set by calling with the new value, ie $object->property() returns, $object->property(“new value”) sets.

the __call() function checks against a list of available variables, so principles of data hiding can be adhered to where required.

this method has the added advantage of being able to overwrite this default behaviour by adding in any other function, as in the requirement above of adding in a new filter/modifier on a property.

the __call() function can be seen at http://pastebin.com/f28429455. the code is ripped out of my current DataObject class and has some additional code to allow all objects to return the objects ID and load status.

By: Federico

Federico — Mon, 18 Aug 2008 12:27:20 +0000

@Radoslav: Yes, that’s a valid example. It’s similar to the one I posted before. And that’s exactly the point, to show how useful the property construct is.

By: Radoslav Stankov

Radoslav Stankov — Mon, 18 Aug 2008 12:11:45 +0000

may be something like this(a very dirty and slow, but will work)

http://codepad.org/75ZWvYI7

By: Federico

Federico — Mon, 18 Aug 2008 11:49:37 +0000

@Sam: Yes, but what happens if a new variable is introduced, for example, author? Here’s your example: http://codepad.org/3jj562He

1. You are converting all the values to lower-case. That’s not part of the requirement.
2. The callers of the class are accessing an attribute that was never implemented: author.

An object should store its state in variables and expose its behaviour through methods, that’s a fundamental principle in object-oriented programming.

By: Sam

Sam — Mon, 18 Aug 2008 10:22:20 +0000

class Book {
private $properties;

function __get($property) {
return strtolower($this->properties[$property]);
}

function __set($property, $value) {
$this->properties[$property] = $value;
}
}

$book = new Book();
$book->title = ‘Code Complete’;
echo $book->title;