Function to import module to namespace

[John Machin]

On Jun 30, 11:45 am, bvdp <b... at mellowood.ca> wrote:
> John Machin wrote:
>
> <snip>
>
> Good questions. Short answer ... probably 'cause I've not thought the
> problem though completely :)
>
>  > You are updating with *everything* in the 'more' module, not just the
>  > functions. This includes such things as __name__, __doc__, __file__.
>  > Could have interesting side-effects.
>  >
>  > One quick silly question: why do you want to do this anyway?
>  >
>
> I'm writing a "simple" macro expander. I've got some mainline code which
> reads an input file, parses out macros, and expands them. So, in my
> input file I might have something like:
>
>       a fjas j kj sdklj sdkl jfsdkl [ link somewhere sometext ]
>
> So, I need a function link() to evaluate and return "http://...."
>
> Instead of putting funcs like link() in my mainline I've stuck them in a
> module of their own.

Why? Do they have any use at all other than to be called by your
mainline?

>  In the mainline I
>
>     import funcs
>
> and then when I need to expand I have the following code:
>

Build a dictionary *ONCE*, not each time you want to look in it. E.g.

funcs_vars = vars(funcs)

... much later:

if not cmd in funcs_vars:


> if not cmd in vars(funcs):
>          error("Unknown function/variable '%s'" % cmd)
>
>      if type(vars(funcs)[cmd]) == type(parse):
>          txt = eval("""funcs.%s("%s")""" % (cmd, arg))

Any particular reason why you are going to the trouble of laboriously
building a statement, compiling it, and running it, when you could
simply do:
   txt = funcs_vars[cmd](arg)
?
>
>      else:   # not a func, just expand the variable
>          if arg:
>              error("Argument to variable '%s' not permitted." % cmd)
>          txt = str(eval("funcs.%s" % cmd ))

   txt = str(funcs_vars[cmd])

>
> Of course, the question comes up ... what if a user (probably me) wants
> to add more functions? Easy enough to just edit funcs.py I suppose, but
> I thought it'd be nice to use more modules.

You may already have one more module than you need.  If the only thing
different about the extra functions is that they are an afterthought,
then put them in the same module as the others.

>
> So, I suppose that rather than adding the 2ndary module stuff to the
> default 'funcs.py' I could just as well have a look and check for the
> needed function in all the modules I've imported.

Sounds quite unnecessary, inefficient and pointless to me.

>
> > Sorry, *two* quick silly questions: are the add-on modules under your
> > control, or do you want to be able to do this with arbitrary modules?
> > [If under your control, you could insist that such modules had an
> > __all__ attribute with appropriate contents]
>
> Why would I want to do that ... and how?

Why: so that you append only the functions that you want to the target
namespace, and don't import stuff like __name__. How: read about
__all__. Just append the stuff that's listed in __all__. However it
sounds like you have seen the light and won't be doing anything like
appending to a namespace.

>
> > A third: why do you want to import into an existing namespace? Now
> > that you know about __import__, why just not call the functions where
> > they are?
>
> Yeah, that would probably be cleaner (safer).

Much cleaner, safer, etc is just to import, or even not to have a
separate module at all.

HTH,
John