Re: Difference between type and class

Thomas Troeger <thomas.troeger.ext@xxxxxxxxxxx> writes:
Can someone explain to me the difference between a type and a class?

If your confusion is of a more general nature I suggest reading the
introduction of `Design Patterns' (ISBN-10: 0201633612), under
Specifying Object Interfaces'.

In short: A type denotes a certain interface, i.e. a set of
signatures, whereas a class tells us how an object is implemented
(like a blueprint). A class can have many types if it implements all
their interfaces, and different classes can have the same type if they
share a common interface. The following example should clarify
matters:

class A:
def bar(self):
print "A"

class B:
def bar(self):
print "B"

class C:
def bla(self):
print "C"

def foo(x):
x.bar()

you can call foo with instances of both A and B, because both classes
share a common type, namely the type that has a `bar' method), but not
with an instance of C because it has no method `bar'. Btw, this
example shows the use of duck typing
(http://en.wikipedia.org/wiki/Duck_typing).

That would imply that I cannot create instances of a type, only of
a class that implements the type, wouldn't it?

But Python denotes 'int' as a type *and* I can instantiate it.



Still confused,

-Nikolaus

--
»It is not worth an intelligent man's time to be in the majority.
By definition, there are already enough people to do that.«
-J.H. Hardy

PGP fingerprint: 5B93 61F8 4EA2 E279 ABF6 02CF A9AD B7F8 AE4E 425C
.

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