Add itershuffle utility function. Maybe belongs in thinc

spacy/util.py

@@ -9,6 +9,7 @@ import regex as re
 from pathlib import Path
 import sys
 import textwrap
+import random
 
 from .symbols import ORTH
 from .compat import cupy, CudaStream, path2str, basestring_, input_, unicode_
@@ -172,6 +173,31 @@ def get_async(stream, numpy_array):
         array.set(numpy_array, stream=stream)
         return array
 
+def itershuffle(iterable, bufsize=1000):
+    """Shuffle an iterator. This works by holding `bufsize` items back
+    and yielding them sometime later. Obviously, this is not unbiased --
+    but should be good enough for batching. Larger bufsize means less bias.
+
+    From https://gist.github.com/andres-erbsen/1307752
+    """
+    iterable = iter(iterable)
+    buf = []
+    try:
+        while True:
+            for i in range(random.randint(1, bufsize-len(buf))):
+                buf.append(iterable.next())
+            random.shuffle(buf)
+            for i in range(random.randint(1, bufsize)):
+                if buf:
+                    yield buf.pop()
+                else:
+                    break
+    except StopIteration:
+        random.shuffle(buf)
+        while buf:
+            yield buf.pop()
+        raise StopIteration
+
 
 def env_opt(name, default=None):
     if type(default) is float: