Simulating call of instance like a list or tuple

[Andrew Bennetts]

On Sun, Jan 13, 2002 at 12:33:52AM -0800, Brett Cannon wrote:
> First, thanks to everyone who replied to my post.
> 
> It seems everyone is thinking that I want __repr__ or __str__, which is in
> the right  vein, but not quite it.  I want the same functionality, but I
> want to be able to return something other than a string.  I don't think it
> exists outside of the built-in classes.

No, __repr__ *is* what you want.

First, let's be perfectly clear -- is this the functionality you are
referring to:

>>> l = [1,2,3]
>>> l
[1, 2, 3]
>>>   

Yes?

Ok, now notice this:

>>> repr(l)
'[1, 2, 3]'

That's right, repr returns the string representation, so that printing the
value from repr:

>>> print repr(l)
[1, 2, 3]

is the same as evaluating the object interactively:

>>> l
[1, 2, 3]

You could also do:

>>> print l
[1, 2, 3]

Note that this isn't "calling" the list -- that would be "l()", which gives
this response:

>>> l() 
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: object of type 'list' is not callable
  
Does this explain things more clearly?  The point here is that the "[1, 2,
3]" you're seeing is not a list, it's the string representation of a list.
I think that's where you're getting confused.

I hope this has helped explain this for you.  If not, please post an example
of where a list behaves differently, and we'll figure out where you (or we)
are getting confused.

-Andrew.