diff -ur patsy-0.5.1/patsy/constraint.py patsy-0.5.1-p39/patsy/constraint.py
--- patsy-0.5.1/patsy/constraint.py	2018-10-28 03:34:36.000000000 +0100
+++ patsy-0.5.1-p39/patsy/constraint.py	2020-01-26 10:58:58.047555461 +0100
@@ -10,7 +10,10 @@
 __all__ = ["LinearConstraint"]
 
 import re
-from collections import Mapping
+try:
+    from collections.abc import Mapping
+except ImportError:
+    from collections import Mapping
 import six
 import numpy as np
 from patsy import PatsyError