import mysteries

[Steven D'Aprano]

On Thu, 21 Jun 2007 16:03:42 -0400, David Abrahams wrote:

> I'm pretty comfortable with Python, but recently I'm constantly finding
> mysterious issues with import.  For example, looking at
> 
>   http://genshi.edgewall.org/browser/trunk/genshi/filters/transform.py
> 
> the examples use the symbol 'HTML' but it's not defined locally, it's
> not explicitly imported, and there's no import *.  Yet doctest will test
> this module and it passes with flying colors.  It turns out HTML is
> defined in genshi.input.  How do I know that?  I grepped for it. How
> does it become available to this module?

There are ways to bypass the import system. The most obvious would be to 
write directly to globals.

>>> spanish_inquisition
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
NameError: name 'spanish_inquisition' is not defined
>>> globals()['spanish_inquisition'] = "NOBODY expects the Spanish 
Inquisition!!!"
>>> spanish_inquisition
'NOBODY expects the Spanish Inquisition!!!'



> Another example: I was recently working on some code that did an import
> from inside a class method.  That import was failing.  I moved the
> import to the top of the file (at module scope) and it succeeded. I'm
> fairly sure that nobody was monkeying around with sys.path in that case.
>  Can anyone think of a likely explanation?

If it was a "from MODULE import *" then it will not work if it is nested 
in a function or class. That's by design.



-- 
Steven.