[Tutor] Iterable Understanding
davea at ieee.org
Mon Nov 16 04:31:11 CET 2009
Marc Tompkins wrote:
> On Sun, Nov 15, 2009 at 4:11 PM, Stephen Nelson-Smith <sanelson at gmail.com>wrote:
>>> import gzip
>>> from heapq import heappush, heappop, merge
>> Is this a preferred method, rather than just 'import heapq'?
>> It has a couple of advantages:
> - convenience: if you "import heapq", then to do a push you need to type
> "heapq.heappush"; if you do "from heapq import heappush", then you can
> simply type "heappush" to use it.
> - efficiency: you import only what you actually need to use. Importing all
from xx import yy, zz gets the whole module xx, not just the
functions yy and zz. It just doesn't add the module name to the
present global namespace. That changes the way you reference yy and zz,
but it doesn't decrease the load time or the memory used. And if you
want to cheat, you can reference the rest of the module with something like:
heapq = sys.modules["heapq"]
which then gets you where you would have been had you just imported the
module the first place.
> of a gigantic package to use one or two methods is wasteful; on the other
> hand, if a package contains five methods and you're using four of them, this
> might not be such a big deal.
Now you switch from talking about modules (heapq) to packages. I don't
believe packages are loaded monolithically, but just modules.
> Remember, this is Python... there's always going to be more than one way to
> do it, and you'll get an argument on this list for every one of them.
> What you should NEVER do, though: "from package import *"
Definite agreement on that one.
Consider the following two lines:
from hashlib import md5
q3 = sys.modules["hashlib"].sha1
Without the first line, the second one gets an error. So the import is
indeed getting more than just the md5 constructor.
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