Tutoral < ? < Language Reference

[Jim Dennis]

In article <3281a460.0204050705.4b9b595f at posting.google.com>, P Adhia wrote:

> Hi,

> I think I have graduated to the next level after reading the tutorial.
> But I find language reference just describing the formal grammer,
> probably meant for programmers who already know python well (rather
> too well). Just as an example, by readking lang. reference I still
> don't know what "..." is and couldn't find refences to __all__,
> __slots__. Is there a "python referece" available somewhere, which
> covers every aspects of python, possibly with explanation+examples
> (something akin to what K&R is for C) ?

>Thanks
>P. Adhia

 ... is an Ellipsis; I gather that there is such a thing as an
 Ellipsis object which I guess is some way of representing 
 recursive references.  For example:

 	a = []; a.append(a)

 ... If you do this from an interactive interpreter session
 and then just type: 

 >>> a

 ... you should get:

 [[...]]

 (a list containing a list containing an Ellipsis object)?

 I won't pretend to understand this; and maybe I'm completely 
 mistaken.  However, this is the impression I've gotten.  As you 
 say, the Tutorials (and other books and docs I've see) don't 
 explain it.

 __all__ is a member of a package which lists "all" of the 
 classes that are intended to be part of the package (exposed via
 the dir() built-in).  It's mostly used in the sorts of modules
 that are implemented as a directory tree, so it would be set 
 in an __init__.py file.  
 
 __slots__ is a special member for 2.2 "New" classes (as opposed
 to "classic classes").  It provides support for constraining the 
 list of attributes for an object.  Basically it means that efforts
 to add new attributes in an object will raise an AttributeError
 exception.  (Unless they are in __slots__ or if the __setattr__
 method of an object handles it for us?).

 """
 Finally, it's possible to constrain the list of attributes that can be
 referenced on an object using the new __slots__ class
 attribute. Python objects are usually very dynamic; at any time it's
 possible to define a new attribute on an instance by just
 doing obj.new_attr=1. This is flexible and convenient, but this
 flexibility can also lead to bugs, as when you meant to write
 obj.template = 'a' but made a typo and wrote obj.templtae by accident. 

 A new-style class can define a class attribute named __slots__ to
 constrain the list of legal attribute names.
 """

 You can read much more about these and other 2.2 features at:

 	http://www.amk.ca/python/2.2/