fix: error if eval()-ing repr(SchemaField) (googleapis#1046)

* fix: error if eval()-ing repr(SchemaField)

* Make repr(PolicyTagList) evaluable

* Fix SchemaField repr with policy tags

The repr() should be evaluable.

Co-authored-by: Tres Seaver <tseaver@palladion.com>

google/cloud/bigquery/schema.py

@@ -268,7 +268,7 @@ def _key(self):
                     field_type = f"{field_type}({self.precision})"
 
         policy_tags = (
-            () if self.policy_tags is None else tuple(sorted(self.policy_tags.names))
+            None if self.policy_tags is None else tuple(sorted(self.policy_tags.names))
         )
 
         return (
@@ -336,7 +336,11 @@ def __hash__(self):
         return hash(self._key())
 
     def __repr__(self):
-        return "SchemaField{}".format(self._key())
+        key = self._key()
+        policy_tags = key[-1]
+        policy_tags_inst = None if policy_tags is None else PolicyTagList(policy_tags)
+        adjusted_key = key[:-1] + (policy_tags_inst,)
+        return f"{self.__class__.__name__}{adjusted_key}"
 
 
 def _parse_schema_resource(info):
@@ -407,7 +411,7 @@ class PolicyTagList(object):
             `projects/*/locations/*/taxonomies/*/policyTags/*`.
     """
 
-    def __init__(self, names=()):
+    def __init__(self, names: Iterable[str] = ()):
         self._properties = {}
         self._properties["names"] = tuple(names)
 
@@ -425,7 +429,7 @@ def _key(self):
         Returns:
             Tuple: The contents of this :class:`~google.cloud.bigquery.schema.PolicyTagList`.
         """
-        return tuple(sorted(self._properties.items()))
+        return tuple(sorted(self._properties.get("names", ())))
 
     def __eq__(self, other):
         if not isinstance(other, PolicyTagList):
@@ -439,7 +443,7 @@ def __hash__(self):
         return hash(self._key())
 
     def __repr__(self):
-        return "PolicyTagList{}".format(self._key())
+        return f"{self.__class__.__name__}(names={self._key()})"
 
     @classmethod
     def from_api_repr(cls, api_repr: dict) -> "PolicyTagList":
@@ -478,5 +482,5 @@ def to_api_repr(self) -> dict:
                 A dictionary representing the PolicyTagList object in
                 serialized form.
         """
-        answer = {"names": [name for name in self.names]}
+        answer = {"names": list(self.names)}
         return answer

tests/unit/test_schema.py

@@ -510,9 +510,30 @@ def test___hash__not_equals(self):
 
     def test___repr__(self):
         field1 = self._make_one("field1", "STRING")
-        expected = "SchemaField('field1', 'STRING', 'NULLABLE', None, (), ())"
+        expected = "SchemaField('field1', 'STRING', 'NULLABLE', None, (), None)"
         self.assertEqual(repr(field1), expected)
 
+    def test___repr__evaluable_no_policy_tags(self):
+        field = self._make_one("field1", "STRING", "REQUIRED", "Description")
+        field_repr = repr(field)
+        SchemaField = self._get_target_class()  # needed for eval  # noqa
+
+        evaled_field = eval(field_repr)
+
+        assert field == evaled_field
+
+    def test___repr__evaluable_with_policy_tags(self):
+        policy_tags = PolicyTagList(names=["foo", "bar"])
+        field = self._make_one(
+            "field1", "STRING", "REQUIRED", "Description", policy_tags=policy_tags,
+        )
+        field_repr = repr(field)
+        SchemaField = self._get_target_class()  # needed for eval  # noqa
+
+        evaled_field = eval(field_repr)
+
+        assert field == evaled_field
+
 
 # TODO: dedup with the same class in test_table.py.
 class _SchemaBase(object):
@@ -786,6 +807,34 @@ def test___hash__not_equals(self):
         set_two = {policy2}
         self.assertNotEqual(set_one, set_two)
 
+    def test___repr__no_tags(self):
+        policy = self._make_one()
+        assert repr(policy) == "PolicyTagList(names=())"
+
+    def test___repr__with_tags(self):
+        policy1 = self._make_one(["foo", "bar", "baz"])
+        policy2 = self._make_one(["baz", "bar", "foo"])
+        expected_repr = "PolicyTagList(names=('bar', 'baz', 'foo'))"  # alphabetical
+
+        assert repr(policy1) == expected_repr
+        assert repr(policy2) == expected_repr
+
+    def test___repr__evaluable_no_tags(self):
+        policy = self._make_one(names=[])
+        policy_repr = repr(policy)
+
+        evaled_policy = eval(policy_repr)
+
+        assert policy == evaled_policy
+
+    def test___repr__evaluable_with_tags(self):
+        policy = self._make_one(names=["foo", "bar"])
+        policy_repr = repr(policy)
+
+        evaled_policy = eval(policy_repr)
+
+        assert policy == evaled_policy
+
 
 @pytest.mark.parametrize(
     "api,expect,key2",