--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/planemo/lib/python3.7/site-packages/lxml/html/_setmixin.py	Fri Jul 31 00:32:28 2020 -0400
@@ -0,0 +1,56 @@
+try:
+    from collections.abc import MutableSet
+except ImportError:
+    from collections import MutableSet
+
+
+class SetMixin(MutableSet):
+
+    """
+    Mix-in for sets.  You must define __iter__, add, remove
+    """
+
+    def __len__(self):
+        length = 0
+        for item in self:
+            length += 1
+        return length
+
+    def __contains__(self, item):
+        for has_item in self:
+            if item == has_item:
+                return True
+        return False
+
+    issubset = MutableSet.__le__
+    issuperset = MutableSet.__ge__
+
+    union = MutableSet.__or__
+    intersection = MutableSet.__and__
+    difference = MutableSet.__sub__
+    symmetric_difference = MutableSet.__xor__
+
+    def copy(self):
+        return set(self)
+
+    def update(self, other):
+        self |= other
+
+    def intersection_update(self, other):
+        self &= other
+
+    def difference_update(self, other):
+        self -= other
+
+    def symmetric_difference_update(self, other):
+        self ^= other
+
+    def discard(self, item):
+        try:
+            self.remove(item)
+        except KeyError:
+            pass
+
+    @classmethod
+    def _from_iterable(cls, it):
+        return set(it)