Ben Finney wrote: > Ned Batchelder <n...@nedbatchelder.com> writes: > >> On 1/27/15 3:12 PM, Mario Figueiredo wrote: >> > This is a follow up from a previous discussion in which it is argued >> > that the following code produces the correct error message terminology, >> > considering that in Python an object is also an instance. >> >> I don't know what the difference is between "object" and "instance". >> An object is an instance of a class. The two words are >> interchangeable as far as I know. > > Not in English grammar, IMO. To say “foo is an instance” implies the > sentence isn't finished; the term “instance” only makes sense in the > context of a relationship to some class. To say “foo is an object” > doesn't have that implication.
I'm sure that there is a grammatical term for this, but I don't know it. Regardless of the terminology though, "foo is an instance" is a complete sentence fragment: "foo is an instance" (of some unspecified class) is the same grammatical construct as: "George is a soldier" (of some unspecified army) "Pluto is a cartoon animal" (of some unspecified species) "Bearhugger's Old Peculiar is a drink" (of some unspecified type) "Herbie is a car" (of some unspecified make and model) etc. In Java, the term "object" as a synonym for "instance" is unambiguous, because in Java all classes are subclasses of Object, and no classes are themselves instances of a class. But that's not the case with Python. >> A common mistake is to believe that "OOP" is a well-defined term. >> It's not it's a collection of ideas that are expressed slightly >> differently in each language. > > Right. The common meaning of “object” shared by all OOP systems is > surprisingly small. Agreed. There really is no widespread agreement on what OOP means *precisely*. Wikipedia states: "Attempts to find a consensus definition or theory behind objects have not proven very successful" and there is little agreement of the fundamental features of OOP: http://en.wikipedia.org/wiki/Object- oriented_programming#Fundamental_features_and_concepts [...] > In Python, every class is an object. Every class has the full range of > behaviour that we expect of objects. A class just has the additional > feature that it can be instantiated. We can also define an "is-a" relationship between classes and their instances: [1, 2, "spam"] is-a list; but not list is-a [1, 2, "spam"] However, in Python that breaks down at the very bottom of the inheritance hierarchy, thanks to the circular relationship between type and object: py> isinstance(type, object) True py> isinstance(object, type) True type is-a object object is-a type -- Steve -- https://mail.python.org/mailman/listinfo/python-list
