Problem with python 3.2 and circular imports

[Frank Millman]

"Ben Finney" <ben+python at benfinney.id.au> wrote in message 
news:87aahh6401.fsf at benfinney.id.au...
> "Frank Millman" <frank at chagford.com> writes:
>
>> Assume the following structure -
>>
>> main.py
>> /pkg
>>    __init__.py
>>    mod1.py
>>    mod2.py
>>
>> main.py
>>    from pkg import mod1
>>
>> mod1.py
>>    import mod2
>>
>> mod2.py
>>  import mod1
>
> What are you expecting the result to be?
>

Simply that mod1 can refer to objects in mod2, and mod2 can refer to objects 
in mod1.

> If it's about sharing objects between the modules, why not break the
> circular dependency: factor out the common code to a module that both
> the others import?
>
>> Any comments or suggestions will be appreciated.
>
> Special cases aren't special enough to break the rules. If you think you
> have a practical reason to do so, it would be best to make it explicit
> when asking for help about this.
>

I am trying to understand what 'the rule' is. Your advice above suggests 
that you are one of those who recommend that circular imports are best 
avoided altogether. In an ideal world I would agree. However, the fact is 
that, no doubt due to a mental block I have, I do find myself in this 
situation from time to time, and I have not seen anything in the 
documentation or other literature that says it is absolutely wrong. 
Therefore, while I do try to avoid circular imports where possible, I would 
also like to know how to manage it in situations where I don't see a simple 
alternative.

>From everything I have read about how the import mechanism works, I don't 
understand *why* the above construct fails. That is actually what I am 
asking for help with.

Thanks

Frank