bpo-35079: Revise difflib.SequenceManager.get_matching_blocks doc (GH-10144)

Specify that blocks are non-overlapping. Change '!=' to '<'.
(cherry picked from commit d9bff4e8)
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Doc/library/difflib.rst

@@ -431,14 +431,15 @@ The :class:`SequenceMatcher` class has this constructor:
 
    .. method:: get_matching_blocks()
 
-      Return list of triples describing matching subsequences. Each triple is of
-      the form ``(i, j, n)``, and means that ``a[i:i+n] == b[j:j+n]``.  The
+      Return list of triples describing non-overlapping matching subsequences.
+      Each triple is of the form ``(i, j, n)``,
+      and means that ``a[i:i+n] == b[j:j+n]``.  The
       triples are monotonically increasing in *i* and *j*.
 
       The last triple is a dummy, and has the value ``(len(a), len(b), 0)``.  It
       is the only triple with ``n == 0``.  If ``(i, j, n)`` and ``(i', j', n')``
       are adjacent triples in the list, and the second is not the last triple in
-      the list, then ``i+n != i'`` or ``j+n != j'``; in other words, adjacent
+      the list, then ``i+n < i'`` or ``j+n < j'``; in other words, adjacent
       triples always describe non-adjacent equal blocks.
 
       .. XXX Explain why a dummy is used!

Misc/NEWS.d/next/Library/2018-10-26-22-53-16.bpo-35079.Tm5jvF.rst

+Improve difflib.SequenceManager.get_matching_blocks doc by adding 'non-
+overlapping' and changing '!=' to '<'.