[C++-sig] Calling import() multiple times for the same module
dave at boostpro.com
Mon Oct 27 22:43:36 CET 2008
on Mon Oct 27 2008, "Robert Dailey" <rcdailey-AT-gmail.com> wrote:
> On Fri, Oct 24, 2008 at 1:07 PM, Stefan Seefeld <seefeld at sympatico.ca> wrote:
> Robert Dailey wrote:
> What happens if I do the following?
> using namespace boost::python;
> import( "__main__" ).attr( "new_global" ) = 40.0f;
> import( "__main__" ).attr( "another_global" ) = 100.0f:
> My main concern here is performance. I'm wondering if each call to
> import() results in a disk query for the script in question and loads it
> from there. I'm also wondering if the second import() above will simply
> read from a memory cache or something.
> As the above code is only a wrapper around the Python runtime, you are really
> asking about how Python handles repeated 'import' calls. I'm pretty sure
> importing a module while it is already imported will do (almost) nothing.
> However, I'm not sure whether a module is actually unloaded as soon as the last
> reference goes away (such as after the first line above is completed), so I
> can't give a definite answer.
> I'm sure you'll get better answers when asking on a Python forum directly.
> I posted about this on the Python mailing list but I'm receiving no responses :(
Python keeps a dictionary in sys.modules that maps module names to
module objects. Import looks there first and doesn't hit the filesystem
if it finds anything.
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