Catch MemoryError better in PE's block matching algo

fixes #264 (for good this time, hopefully)

core_pe/matchblock.py

@@ -193,13 +193,13 @@ def getmatches(pictures, cache_path, threshold=75, match_scaled=False, j=job.nul
         # some wiggle room, log about the incident, and stop matching right here. We then process
         # the matches we have. The rest of the process doesn't allocate much and we should be
         # alright.
-        del matches[-1000:] # some wiggle room to ensure we don't run out of memory again.
-        logging.warning("Ran out of memory when scanning! We had %d matches.", len(matches) + 1000)
+        del comparisons_to_do, chunks, pictures # some wiggle room for the next statements
+        logging.warning("Ran out of memory when scanning! We had %d matches.", len(matches))
+        del matches[-len(matches)//3:] # some wiggle room to ensure we don't run out of memory again.
     pool.close()
-
     result = []
     myiter = j.iter_with_progress(
-        iterconsume(matches),
+        iterconsume(matches, reverse=False),
         tr("Verified %d/%d matches"),
         every=10,
         count=len(matches),

hscommon/tests/util_test.py

@@ -65,6 +65,12 @@ def test_trailiter():
     eq_(list(trailiter(['foo', 'bar'], skipfirst=True)), [('foo', 'bar')])
     eq_(list(trailiter([], skipfirst=True)), []) # no crash
 
+def test_iterconsume():
+    # We just want to make sure that we return *all* items and that we're not mistakenly skipping
+    # one.
+    eq_(list(range(2500)), list(iterconsume(list(range(2500)))))
+    eq_(list(reversed(range(2500))), list(iterconsume(list(range(2500)), reverse=False)))
+
 #--- String
 
 def test_escape():

hscommon/util.py

@@ -117,23 +117,20 @@ def trailiter(iterable, skipfirst=False):
         yield prev, item
         prev = item
 
-def iterconsume(seq):
-    """Iterate over ``seq`` and discard yielded objects.
+def iterconsume(seq, reverse=True):
+    """Iterate over ``seq`` and pops yielded objects.
 
-    Right after the ``yield``, we replace the element we've just yielded by ``None`` in the
-    sequence.
+    Because we use the ``pop()`` method, we reverse ``seq`` before proceeding. If you don't need
+    to do that, set ``reverse`` to ``False``.
 
     This is useful in tight memory situation where you are looping over a sequence of objects that
     are going to be discarded afterwards. If you're creating other objects during that iteration
     you might want to use this to avoid ``MemoryError``.
-
-    Note that this only works for sequence (index accessible), not all iterables.
     """
-    # We don't use ``del``, because it would be disastrous performance-wise as the array would have
-    # to be constantly re-allocated.
-    for index, elem in enumerate(seq):
-        seq[index] = None
-        yield elem
+    if reverse:
+        seq.reverse()
+    while seq:
+        yield seq.pop()
 
 #--- String related