Issue #1680159: unicode coercion during an 'in' operation was masking
any errors that might occur during coercion of the left operand and
turning them into a TypeError with a message text that was confusing in
the given context.  This patch lets any errors through, as was already
done during coercion of the right hand side.
diff --git a/Misc/NEWS b/Misc/NEWS
index cfdf975..08369a2 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- Issue #1680159: unicode coercion during an 'in' operation no longer masks
+  the underlying error when the coercion fails for the left hand operand.
+
 - Issue #7491: Metaclass's __cmp__ method was ignored.
 
 - Issue #7466: segmentation fault when the garbage collector is called