[Tutor] Questions regarding class documentation ...

[hcohen2]

Because the Core Python Programming book was so out of date regarding 
class and objects discussion I switched over to reading the Alan Gauld 
tutorial on the topic; afterward I directed my attention to the 
documentation on the python.org site.

[ Here are some facts to keep in mind as you read the discussion below: 
documentation was for version 2.2.3 and I am using 2.2.2.  I have so far 
reproduced the results exactly when I ran it interactively.  I am trying 
to prepare myself to create applications independently, hence, I try to 
go beyond the text samples and use more general approaches.]

Rather than running the code, in section: Subclassing built-in types,  
interactively I pasted the class definition in a file.  Moreover, to 
keep it general I gave the file a name different from the class defined 
in the file, since I would expect I would have many unrelated class 
definitions within a single file that I would load to run a custom 
application.

So within the python interpreter I imported the file containing the 
defaultdict class:

 >>>import sampledict  # name sampledict.py

however, when I attempted to run the sample code in the documentation:

 >>> print defaultdict
...
NameError: name 'defaultdict' is not defined

Running dir() shows, indeed, 'sampledict' is listed but not 
'defaultdict, despite the importing of the file that contains the 
latter's definition.

Perhaps what I did next was due to my having a tenuous grasp on this 
topic I remembered the problems with unbound method discussion.  Hence, 
I tried to created an instance, but I got the same error.  At that point 
I became suspicious of the success the importing command.  Though I know 
it is bad style and a command to be avoided I gave the command:

 >>> from sampledict import defaultdict
 >>> print defaultdict
<class 'sampledict.defaultdict'>
 >>> dictIns = defaultdict()
 >>> print dictIns
{}
 >>> type(dictIns)
<class 'sampledict.defaultdict'>

Now the print dictIns 'works', but I have a number of questions!

Again the interactive reproduction of the code works exactly as 
described (as far as I have gone).  While I can reproduce the results, 
why doesn't the simple import command work for the file?  What happened 
to seeing an instance rather than the type now being class for dictIns?

Could someone enlighten me regarding these questions without citing 
further documentation that might just add to my confusion as to what may 
be happening.  When I created instances previously that were identified 
as instances not as a class.  [Regarding the last statement: on this 
machine with this version of Python.]

It is very difficult to gain a firm grasp of this topic when the results 
are so haphazard and not internally consistent.

I would like to thank anyone that can clarify why I have run into these 
difficulties.