On 2/7/2012 9:35 PM, PJ Eby wrote:
On Tue, Feb 7, 2012 at 6:40 PM, Terry Reedy <tjre...@udel.edu <mailto:tjre...@udel.edu>> wrote:importlib could provide a parameterized decorator for functions that are the only consumers of an import. It could operate much like this: def imps(mod): def makewrap(f): def wrapped(*args, **kwds): print('first/only call to wrapper') g = globals() g[mod] = __import__(mod) g[f.__name__] = f f(*args, **kwds) wrapped.__name__ = f.__name__ return wrapped return makewrap @imps('itertools') def ic(): print(itertools.count) ic() ic() # first/only call to wrapper <class 'itertools.count'> <class 'itertools.count'> If I were going to rewrite code, I'd just use lazy imports (see http://pypi.python.org/pypi/Importing ). They're even faster than this approach (or using plain import statements), as they have zero per-call function call overhead.
My code above and Importing, as I understand it, both delay imports until needed by using a dummy object that gets replaced at first access. (Now that I am reminded, sys.modules is the better place for the dummy objects. I just wanted to show that there is a simple solution (though more specialized) even for existing code.) The cost of delay, which might mean never, is a bit of one-time extra overhead. Both have no extra overhead after the first call. Unless delayed importing is made standard, both require a bit of extra code somewhere.
It's just that not everything I write can depend on Importing. Throw an equivalent into the stdlib, though, and I guess I wouldn't have to worry about dependencies...
And that is what I think (agree?) should be done to counteract the likely slowdown from using importlib.
(To be clearer; I'm talking about the http://peak.telecommunity.com/DevCenter/Importing#lazy-imports feature, which sticks a dummy module subclass instance into sys.modules, whose __gettattribute__ does a reload() of the module, forcing the normal import process to run, after first changing the dummy object's type to something that doesn't have the __getattribute__ any more. This ensures that all accesses after the first one are at normal module attribute access speed. That, and the "whenImported" decorator from Importing would probably be of general stdlib usefulness too.)
-- Terry Jan Reedy _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
