workaround a bug with the ast unparse package and Python 3.8

lale/expressions.py

@@ -19,6 +19,7 @@
 from typing import Any, Dict, Optional, Union
 
 import astunparse
+from six.moves import cStringIO
 
 AstLits = (ast.Num, ast.Str, ast.List, ast.Tuple, ast.Set, ast.Dict)
 AstLit = Union[ast.Num, ast.Str, ast.List, ast.Tuple, ast.Set, ast.Dict]
@@ -48,6 +49,27 @@
 ]
 
 
+# !! WORKAROUND !!
+# There is a bug with astunparse and Python 3.8.
+# https://github.com/simonpercivall/astunparse/issues/43
+# Until it is fixed (which may be never), here is a workaround,
+# based on the workaround found in https://github.com/juanlao7/codeclose
+class FixUnparser(astunparse.Unparser):
+    def _Constant(self, t):
+        if not hasattr(t, "kind"):
+            setattr(t, "kind", None)
+
+        super()._Constant(t)
+
+
+# !! WORKAROUND !!
+# This method should be called instead of astunparse.unparse
+def fixedUnparse(tree):
+    v = cStringIO()
+    FixUnparser(tree, file=v)
+    return v.getvalue()
+
+
 class Expr:
     _expr: AstExpr
 
@@ -104,7 +126,7 @@ def __getitem__(self, key: Union[int, str, slice]) -> "Expr":
         return Expr(subscript)
 
     def __str__(self) -> str:
-        result = astunparse.unparse(self._expr).strip()
+        result = fixedUnparse(self._expr).strip()
         if isinstance(self._expr, (ast.UnaryOp, ast.BinOp, ast.Compare, ast.BoolOp)):
             if result.startswith("(") and result.endswith(")"):
                 result = result[1:-1]

test/test_core_misc.py

@@ -62,6 +62,19 @@ def test_transformers(self):
         self.assertNotIn("MLPClassifier", ops_names)
 
 
+class TestUnparseExpr(unittest.TestCase):
+    def test_unparse_const38(self):
+        import lale.expressions
+        from lale.expressions import it
+
+        test_expr = it.hello["hi"]
+        # This fails on 3.8 with some versions of the library
+        # which is why we use the fixed version
+        # import astunparse
+        # astunparse.unparse(he._expr)
+        str(lale.expressions.fixedUnparse(test_expr._expr))
+
+
 class TestOperatorWithoutSchema(unittest.TestCase):
     def test_trainable_pipe_left(self):
         from sklearn.decomposition import PCA