--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.7/site-packages/cwltool/flatten.py	Thu May 14 14:56:58 2020 -0400
@@ -0,0 +1,27 @@
+from __future__ import absolute_import
+
+from typing import Any, Callable, List, Text, cast
+
+# http://rightfootin.blogspot.com/2006/09/more-on-python-flatten.html
+
+
+def flatten(l, ltypes=(list, tuple)):
+    # type: (Any, Any) -> List[Any]
+    if l is None:
+        return []
+    if not isinstance(l, ltypes):
+        return [l]
+
+    ltype = type(l)
+    l = list(l)
+    i = 0
+    while i < len(l):
+        while isinstance(l[i], ltypes):
+            if not l[i]:
+                l.pop(i)
+                i -= 1
+                break
+            else:
+                l[i:i + 1] = l[i]
+        i += 1
+    return cast(Callable[[Any], List[Any]], ltype)(l)