How should I expose read-only fields from Python classes?

Question

I have many different small classes which have a few fields each, e.g. this:

class Article:
    def __init__(self, name, available):
        self.name = name         


        

Answer 1

Based in the Chris answer, but arguably more pythonic:

def ro_property(field):
    return property(lambda self : self.__dict__[field])

class Article(object):
    name = ro_property('_name')

    def __init__(self):
        self._name = "banana"

If trying to modify the property it will raise an AttributeError.

a = Article()
print a.name # -> 'banana'
a.name = 'apple' # -> AttributeError: can't set attribute

UPDATE: About your updated answer, the (little) problem I see is that you are modifying the definition of the property in the class every time you create an instance. And I don't think that is such a good idea. That's why I put the ro_property call outside of the __init__ function

What about?:

def ro_property(name):
    def ro_property_decorator(c):
        setattr(c, name, property(lambda o: o.__dict__["_" + name]))
        return c
    return ro_property_decorator

@ro_property('name')
@ro_property('other')
class Article(object):
    def __init__(self, name):
        self._name = name
        self._other = "foo"

a = Article("banana")
print a.name # -> 'banana'
a.name = 'apple' # -> AttributeError: can't set attribute

Class decorators are fancy!