import from question

[Steven D'Aprano]

On Wed, 16 Jan 2008 15:31:54 -0800, Tobiah wrote:

>> Again, those aren't copies. There is only one instance of each value,
>> referenced by multiple names.
> 
> 
> Ok, I get it.  I was locally importing a pointer to an integer 

Really? What language were you using? Python doesn't have pointers.

Some *implementations* of Python (e.g. CPython) might have pointers *in 
the implementation*, but others (e.g. PyPy, Jython) don't.


> which is
> really the same object as the module name points to, but the assignment
> changes that. The confusion for me centered around the fact that a local
> name can be used to change values in mutables that are visible from
> within the module.  This however, does not include assignment to the
> local name.


If you haven't already done so, you should read:

http://effbot.org/zone/python-objects.htm
http://effbot.org/zone/call-by-object.htm


and remember that imports are (more or less) equivalent to assignments. 
When you do this:

>>> import module

it is roughly equivalent to:

>>> module = get_a_module_from_file_name('module')

Alternatively:

>>> from module import foo

is roughly equivalent to:

>>> temp = get_a_module_from_file_name('module')
>>> foo = temp.foo
>>> del temp


(and the magic function "get_a_module_from_file_name" is actually called 
__import__ with double underscores.)


-- 
Steven