--- difflib.py	Tue Jul 21 02:09:16 2015
+++ difflib_improved.py	Thu Aug 20 17:07:54 2015
@@ -32,6 +32,7 @@
 
 from heapq import nlargest as _nlargest
 from collections import namedtuple as _namedtuple
+from timeit import default_timer as _default_timer
 
 Match = _namedtuple('Match', 'a b size')
 
@@ -117,7 +118,7 @@
 
     Methods:
 
-    __init__(isjunk=None, a='', b='')
+    __init__(isjunk=None, a='', b='', autojunk=True, timeout=0, fallthrough=0))
         Construct a SequenceMatcher.
 
     set_seqs(a, b)
@@ -139,7 +140,7 @@
         Return list of 5-tuples describing how to turn a into b.
 
     ratio()
-        Return a measure of the sequences' similarity (float in [0,1]).
+        Return a measure of the sequences' similarity (float in [0,1] or -1 on timeout).
 
     quick_ratio()
         Return an upper bound on .ratio() relatively quickly.
@@ -148,7 +149,7 @@
         Return an upper bound on ratio() very quickly.
     """
 
-    def __init__(self, isjunk=None, a='', b='', autojunk=True):
+    def __init__(self, isjunk=None, a='', b='', autojunk=True, timeout=0, fallthrough=0):
         """Construct a SequenceMatcher.
 
         Optional arg isjunk is None (the default), or a one-argument
@@ -170,6 +171,19 @@
         Optional arg autojunk should be set to False to disable the
         "automatic junk heuristic" that treats popular elements as junk
         (see module documentation for more information).
+
+        Optional arg timeout should be set to the number of seconds to wait
+        for ratio() or quick_ratio() to complete.  If a timeout seconds is
+        exceeded return -1 for the ratio unless fallthrough is set. This value
+        can be a float.
+
+        Optional arg fallthrough should be set to 1 or 2. If ratio() is
+        called and fallthrough is set to 1, quick_ratio() will be 
+        subsequently called when a timeout occurs. real_quick_ratio()
+        will be called if timeout is set to 2 if another timeout
+        occurs. If quick_ratio() is initially called and fallthrough
+        is set to 1 or 2, real_quick_ratio() will be called when a
+        timeout occurs.
         """
 
         # Members:
@@ -206,11 +220,21 @@
         #      the items in b for which isjunk is True.
         # bpopular
         #      nonjunk items in b treated as junk by the heuristic (if used).
+        # timeout
+        #      number of seconds to wait for ratio() or quick_ratio() to complete
+        # fallthrough
+        #      when ratio() or quick_ratio() times out, fall through to next
+        #      1 or 2 comparison methods: quick_ratio() and then real_quick_ratio()
+        # abort_ratio
+        #      used to keep track of a timeout occurence in ratio()
 
         self.isjunk = isjunk
         self.a = self.b = None
         self.autojunk = autojunk
         self.set_seqs(a, b)
+        self.timeout = timeout
+        self.fallthrough = fallthrough
+        self.abort_ratio = False
 
     def set_seqs(self, a, b):
         """Set the two sequences to be compared.
@@ -396,7 +420,11 @@
         # junk-free match ending with a[i-1] and b[j]
         j2len = {}
         nothing = []
+        start_time = _default_timer()
         for i in range(alo, ahi):
+            if self.timeout and (_default_timer() - start_time) > self.timeout:
+                self.abort_ratio = True
+                return (alo, blo, 0)
             # look at all instances of a[i] in b; note that because
             # b2j has no junk keys, the loop is skipped if a[i] is junk
             j2lenget = j2len.get
@@ -474,9 +502,13 @@
         # at the end.
         queue = [(0, la, 0, lb)]
         matching_blocks = []
+        start_time = _default_timer()
         while queue:
             alo, ahi, blo, bhi = queue.pop()
             i, j, k = x = self.find_longest_match(alo, ahi, blo, bhi)
+            if self.timeout and (_default_timer() - start_time) > self.timeout:
+                self.abort_ratio = True
+                return []
             # a[alo:i] vs b[blo:j] unknown
             # a[i:i+k] same as b[j:j+k]
             # a[i+k:ahi] vs b[j+k:bhi] unknown
@@ -642,6 +674,12 @@
         """
 
         matches = sum(triple[-1] for triple in self.get_matching_blocks())
+        if self.abort_ratio:
+            if self.fallthrough > 0:
+                self.fallthrough -= 1
+                return self.quick_ratio()
+            else:
+                return -1
         return _calculate_ratio(matches, len(self.a) + len(self.b))
 
     def quick_ratio(self):
@@ -663,7 +701,13 @@
         # number of times we've seen it in 'a' so far ... kinda
         avail = {}
         availhas, matches = avail.__contains__, 0
+        start_time = _default_timer()
         for elt in self.a:
+            if self.timeout and (_default_timer() - start_time) > self.timeout:
+                    if self.fallthrough > 0:
+                        return self.real_quick_ratio()
+                    else:
+                        return -1
             if availhas(elt):
                 numb = avail[elt]
             else: