Nice way to cast a homogeneous tuple

[Steven D'Aprano]

On Wed, 28 Jul 2010 09:35:52 -0400, wheres pythonmonks wrote:

> Thanks ... I thought int was a type-cast (like in C++) so I assumed I
> couldn't reference it.

Python doesn't have type-casts in the sense of "tell the compiler to 
treat object of type A as type B instead". The closest Python has to that 
is that if you have an instance of class A, you can do this:

a = A()  # make an instance of class A
a.__class__ = B  # tell it that it's now class B

and hope that it won't explode when you try to use it :/

I make that seem like a dangerous thing to do, but it's not really. There 
actually are sensible use-cases for such a thing, you can't do it to 
built-ins (which would be dangerous!), and the worst that will happen 
with classes written in Python is they'll raise an exception when you try 
calling a method, rather than dump core.

Otherwise, all type conversions in Python create a new instance of the 
new type, and the conversion functions themselves (int, str, etc.) are 
actual type objects which you can pass around to functions:

>>> type(int)
<type 'type'>

Calling int(x) calls the int constructor with argument x, and returns a 
new int object. (In the *specific* case of int, it will sometimes cache 
small integers and re-use the same one multiple times, but don't count on 
that behaviour since it's an implementation-specific optimization.)


-- 
Steven