On Sun, 28 Feb 2021 at 01:19, Cameron Simpson <c...@cskk.id.au> wrote: > My object represents an MDAT box in an MP4 file: it is the ludicrously > large data box containing the raw audiovideo data; for a TV episode it > is often about 2GB and a movie is often 4GB to 6GB. > [...] > That length is presented via the object's __len__ method > [...] > > I noticed that it was stalling, and investigation revealed it was > stalling at this line: > > subboxes = list(self) > > when doing the MDAT box. That box (a) has no subboxes at all and (b) has > a very large __len__ value. > > BUT... It also has a __iter__ value, which like any Box iterates over > the subboxes. For MDAT that is implemented like this: > > def __iter__(self): > yield from () > > What I was expecting was pretty much instant construction of an empty > list. What I was getting was a very time consuming (10 seconds or more) > construction of an empty list.
I can't reproduce, Am I missing something? marco@buzz:~$ python3 Python 3.6.9 (default, Jan 26 2021, 15:33:00) [GCC 8.4.0] on linux Type "help", "copyright", "credits" or "license" for more information. >>> class A: ... def __len__(self): ... return 1024**3 ... def __iter__(self): ... yield from () ... >>> a = A() >>> len(a) 1073741824 >>> list(a) [] >>> It takes milliseconds to run list(a) -- https://mail.python.org/mailman/listinfo/python-list
