Python equivalent for C module

Gary Herron gherron at islandtraining.com
Mon Oct 20 19:28:15 CEST 2008


Derek Martin wrote:
> I'd like to know if it's possible to code something in Python which
> would be equivalent to the following C:
>
> [Assume bool is typedef'd to int, and TRUE and FALSE are #defined to 1
> and 0, respectively]
>
> ---- debug.c ----
> #include <stdio.h>
>
> bool DEBUG;
>
> void dprint(char *msg)
> {
> 	if (DEBUG){
> 		printf("DEBUG: %s", msg);
> 	}
> }
>
> ---- end of debug.c ----
>
> The idea being that all modules of the program would "import" this
> code via the header file:
>
> ---- debug.h ----
> extern bool DEBUG;
> void dprint(char *msg);
> ---- end of debug.h ----
>
> I'm specifically trying to avoid having to create a debug object and
> pass it around... All modules should have visibility into the state of
> whether DEBUG is turned on or off, and be able to use dprint().  Can
> Python do this?
>
> I tried creating debug.py as such:
>
> ---- debug.py ----
> DEBUG = True
> def dprint(msg):
>     if DEBUG:
>         print("DEBUG: %s" % msg)
> ---- end ----
>
> Then in the modules that wanted to use it, I did:
>
> from debug import DEBUG, dprint
>   


So don't import it that way.  Instead, do it this way:

  import debug

Then us like this:
  debug.DEBUG = True
and
  debug.dprint(...)

Lots of other possibilities exist -- but this solves your specific first
question.

> But I got some weird behavior.  The imported copy of DEBUG is
> read-only; if you update it, the name DEBUG points to a different
> object which the other modules can't see.  After doing some reading of
> the docs, this behavior is explained and understood (though obviously
> not what I want).  It just occured to me that I might be able to get
> around that by using a setter function in the module itself... I'll
> try this later. 
>
> The other weird behavior was, once I changed the value of DEBUG,
> dprint() started to behave oddly.  No matter what I passed as an
> argument (and no matter what I set the value of DEBUG to be), it
> started printing the exact literal string:
>
> DEBUG: %s
>
> whenever it was called.  It was as if the function couldn't see the
> parameter msg, which was passed via the call.  Most unexpected, and
> definitely undesirable.
>   


I don't believe it -- send your *actual* code, and we'll all have a look.



Gary Herron

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