AVRO-1737 Implement Hashable Schema

A hashable thing can be a member of a set or a key in a dictionary.

lang/py/avro/schema.py

@@ -247,6 +247,10 @@ def match(self, writer: "Schema") -> bool:
         @return bool
         """
 
+    def __hash__(self) -> int:
+        """Make it so a schema can be in a set or a key in a dictionary."""
+        return hash(self.fingerprint())
+
     def __str__(self) -> str:
         return json.dumps(self.to_json())
 
@@ -288,13 +292,6 @@ def canonical_form(self) -> str:
         # The separators eliminate whitespace around commas and colons.
         return json.dumps(self.to_canonical_json(), separators=(",", ":"))
 
-    @abc.abstractmethod
-    def __eq__(self, that: object) -> bool:
-        """
-        Determines how two schema are compared.
-        Consider the mixins EqualByPropsMixin and EqualByJsonMixin
-        """
-
     def fingerprint(self, algorithm="CRC-64-AVRO") -> bytes:
         """
         Generate fingerprint for supplied algorithm.
@@ -323,6 +320,8 @@ def fingerprint(self, algorithm="CRC-64-AVRO") -> bytes:
 class NamedSchema(Schema):
     """Named Schemas specified in NAMED_TYPES."""
 
+    __hash__ = Schema.__hash__
+
     def __init__(
         self,
         type_: str,
@@ -478,6 +477,8 @@ def to_canonical_json(self, names=None):
 class PrimitiveSchema(EqualByPropsMixin, Schema):
     """Valid primitive types are in PRIMITIVE_TYPES."""
 
+    __hash__ = Schema.__hash__
+
     _validators = {
         "null": lambda x: x is None,
         "boolean": lambda x: isinstance(x, bool),
@@ -540,6 +541,8 @@ def validate(self, datum):
 
 
 class BytesDecimalSchema(PrimitiveSchema, DecimalLogicalSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, precision, scale=0, other_props=None):
         DecimalLogicalSchema.__init__(self, precision, scale, max_precision=((1 << 31) - 1))
         PrimitiveSchema.__init__(self, "bytes", other_props)
@@ -567,6 +570,8 @@ def validate(self, datum):
 # Complex Types (non-recursive)
 #
 class FixedSchema(EqualByPropsMixin, NamedSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, name, namespace, size, names=None, other_props=None, validate_names: bool = True):
         # Ensure valid ctor args
         if not isinstance(size, int) or size < 0:
@@ -618,6 +623,8 @@ def validate(self, datum):
 
 
 class FixedDecimalSchema(FixedSchema, DecimalLogicalSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(
         self,
         size,
@@ -653,6 +660,8 @@ def validate(self, datum):
 
 
 class EnumSchema(EqualByPropsMixin, NamedSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(
         self,
         name: str,
@@ -740,6 +749,8 @@ def validate(self, datum):
 
 
 class ArraySchema(EqualByJsonMixin, Schema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, items, names=None, other_props=None, validate_names: bool = True):
         # Call parent ctor
         Schema.__init__(self, "array", other_props, validate_names=validate_names)
@@ -793,6 +804,8 @@ def validate(self, datum):
 
 
 class MapSchema(EqualByJsonMixin, Schema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, values, names=None, other_props=None, validate_names: bool = True):
         # Call parent ctor
         Schema.__init__(self, "map", other_props, validate_names=validate_names)
@@ -845,6 +858,7 @@ def validate(self, datum):
 
 
 class UnionSchema(EqualByJsonMixin, Schema):
+    __hash__ = Schema.__hash__
     """
     names is a dictionary of schema objects
     """
@@ -916,6 +930,8 @@ def validate(self, datum):
 
 
 class ErrorUnionSchema(UnionSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, schemas, names=None, validate_names: bool = True):
         # Prepend "string" to handle system errors
         UnionSchema.__init__(self, ["string"] + schemas, names, validate_names)
@@ -934,6 +950,8 @@ def to_json(self, names=None):
 
 
 class RecordSchema(EqualByJsonMixin, NamedSchema):
+    __hash__ = Schema.__hash__
+
     @staticmethod
     def make_field_objects(field_data: Sequence[Mapping[str, object]], names: avro.name.Names, validate_names: bool = True) -> Sequence[Field]:
         """We're going to need to make message parameters too."""
@@ -1068,6 +1086,8 @@ def validate(self, datum):
 
 
 class DateSchema(LogicalSchema, PrimitiveSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, other_props=None):
         LogicalSchema.__init__(self, avro.constants.DATE)
         PrimitiveSchema.__init__(self, "int", other_props)
@@ -1086,6 +1106,8 @@ def validate(self, datum):
 
 
 class TimeMillisSchema(LogicalSchema, PrimitiveSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, other_props=None):
         LogicalSchema.__init__(self, avro.constants.TIME_MILLIS)
         PrimitiveSchema.__init__(self, "int", other_props)
@@ -1104,6 +1126,8 @@ def validate(self, datum):
 
 
 class TimeMicrosSchema(LogicalSchema, PrimitiveSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, other_props=None):
         LogicalSchema.__init__(self, avro.constants.TIME_MICROS)
         PrimitiveSchema.__init__(self, "long", other_props)
@@ -1122,6 +1146,8 @@ def validate(self, datum):
 
 
 class TimestampMillisSchema(LogicalSchema, PrimitiveSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, other_props=None):
         LogicalSchema.__init__(self, avro.constants.TIMESTAMP_MILLIS)
         PrimitiveSchema.__init__(self, "long", other_props)
@@ -1139,6 +1165,8 @@ def validate(self, datum):
 
 
 class TimestampMicrosSchema(LogicalSchema, PrimitiveSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, other_props=None):
         LogicalSchema.__init__(self, avro.constants.TIMESTAMP_MICROS)
         PrimitiveSchema.__init__(self, "long", other_props)
@@ -1156,6 +1184,8 @@ def validate(self, datum):
 
 
 class UUIDSchema(LogicalSchema, PrimitiveSchema):
+    __hash__ = Schema.__hash__
+
     def __init__(self, other_props=None):
         LogicalSchema.__init__(self, avro.constants.UUID)
         PrimitiveSchema.__init__(self, "string", other_props)

lang/py/avro/test/test_schema.py

@@ -890,6 +890,31 @@ def parse_invalid(self):
             self.test_schema.parse()
 
 
+class HashableTestCase(unittest.TestCase):
+    """Ensure that Schema are hashable.
+
+    While hashability is implemented with parsing canonical form fingerprinting,
+    this test should be kept distinct to avoid coupling."""
+
+    def __init__(self, test_schema):
+        """Ignore the normal signature for unittest.TestCase because we are generating
+        many test cases from this one class. This is safe as long as the autoloader
+        ignores this class. The autoloader will ignore this class as long as it has
+        no methods starting with `test_`.
+        """
+        super().__init__("parse_and_hash")
+        self.test_schema = test_schema
+
+    def parse_and_hash(self):
+        """Ensure that every schema can be hashed."""
+        try:
+            hash(self.test_schema.parse())
+        except TypeError as e:
+            if "unhashable type" in str(e):
+                self.fail(f"{self.test_schema} is not hashable")
+            raise
+
+
 class RoundTripParseTestCase(unittest.TestCase):
     """Enable generating round-trip parse test cases over all the valid test schema."""
 
@@ -1434,6 +1459,7 @@ def load_tests(loader, default_tests, pattern):
     suite.addTests(OtherAttributesTestCase(ex) for ex in OTHER_PROP_EXAMPLES)
     suite.addTests(loader.loadTestsFromTestCase(CanonicalFormTestCase))
     suite.addTests(FingerprintTestCase(ex[0], ex[1]) for ex in FINGERPRINT_EXAMPLES)
+    suite.addTests(HashableTestCase(ex) for ex in VALID_EXAMPLES)
     return suite