Implement new default constr ID

integration-test/test/test_plutus.py

@@ -26,7 +26,7 @@ def test_plutus_v1(self):
 
         builder = TransactionBuilder(self.chain_context)
         builder.add_input_address(giver_address)
-        datum = PlutusData()  # A Unit type "()" in Haskell
+        datum = Unit()  # A Unit type "()" in Haskell
         builder.add_output(
             TransactionOutput(script_address, 50000000, datum_hash=datum_hash(datum))
         )

pycardano/plutus.py

@@ -6,6 +6,7 @@
 import json
 from dataclasses import dataclass, field, fields
 from enum import Enum
+from hashlib import sha256
 from typing import Any, ClassVar, Optional, Type, Union
 
 import cbor2
@@ -44,9 +45,16 @@
     "datum_hash",
     "plutus_script_hash",
     "script_hash",
+    "Unit",
 ]
 
 
+# taken from https://stackoverflow.com/a/13624858
+class classproperty(property):
+    def __get__(self, owner_self, owner_cls):
+        return self.fget(owner_cls)
+
+
 class CostModels(DictCBORSerializable):
     KEY_TYPE = int
     VALUE_TYPE = dict
@@ -460,9 +468,31 @@ class will reduce the complexity of serialization and deserialization tremendous
         >>> assert test == Test.from_cbor("d87a9f187b43333231ff")
     """
 
-    CONSTR_ID: ClassVar[int] = 0
-    """Constructor ID of this plutus data.
-       It is primarily used by Plutus core to reconstruct a data structure from serialized CBOR bytes."""
+    AUTO_ID: ClassVar[bool] = False
+    """Enables automatic assignment of a deterministic constructor id (CONSTR_ID) for the Plutus data if set to True."""
+
+    @classproperty
+    def CONSTR_ID(cls):
+        """
+        Constructor ID of this plutus data.
+        It is primarily used by Plutus core to reconstruct a data structure from serialized CBOR bytes.
+        The default implementation is an almost unique, deterministic constructor ID in the range 1 - 2^32 based
+        on class attributes, types and class name.
+        """
+        if not cls.AUTO_ID:
+            return 0
+
+        k = f"_CONSTR_ID_{cls.__name__}"
+        if not hasattr(cls, k):
+            det_string = (
+                cls.__name__
+                + "*"
+                + "*".join([f"{f.name}~{f.type}" for f in fields(cls)])
+            )
+            det_hash = sha256(det_string.encode("utf8")).hexdigest()
+            setattr(cls, k, int(det_hash, 16) % 2**32)
+
+        return getattr(cls, k)
 
     def __post_init__(self):
         valid_types = (PlutusData, dict, IndefiniteList, int, bytes)
@@ -820,3 +850,10 @@ def script_hash(script: ScriptType) -> ScriptHash:
         )
     else:
         raise TypeError(f"Unexpected script type: {type(script)}")
+
+
+@dataclass
+class Unit(PlutusData):
+    """The default "Unit type" with a 0 constructor ID"""
+
+    CONSTR_ID = 0

test/pycardano/test_plutus.py

@@ -1,13 +1,15 @@
 import copy
-import unittest
+import subprocess
+import sys
+import tempfile
 from dataclasses import dataclass
 from test.pycardano.util import check_two_way_cbor
 from typing import Dict, List, Union
 
 import pytest
 from cbor2 import CBORTag
 
-from pycardano.exception import DeserializeException, SerializeException
+from pycardano.exception import DeserializeException
 from pycardano.plutus import (
     COST_MODELS,
     ExecutionUnits,
@@ -51,6 +53,7 @@ class DictTest(PlutusData):
 
 @dataclass
 class ListTest(PlutusData):
+    CONSTR_ID = 0
     a: List[LargestTest]
 
 
@@ -316,3 +319,87 @@ def test_clone_plutus_data():
     my_vesting.deadline = 1643235300001
 
     assert cloned_vesting != my_vesting
+
+
+def test_unique_constr_ids():
+    @dataclass
+    class A(PlutusData):
+        AUTO_ID = True
+        pass
+
+    @dataclass
+    class B(PlutusData):
+        AUTO_ID = True
+        pass
+
+    assert (
+        A.CONSTR_ID != B.CONSTR_ID
+    ), "Different classes (different names) have same default constructor ID"
+    B_tmp = B
+
+    @dataclass
+    class B(PlutusData):
+        AUTO_ID = True
+        a: int
+        b: bytes
+
+    assert (
+        B_tmp.CONSTR_ID != B.CONSTR_ID
+    ), "Different classes (different fields) have same default constructor ID"
+
+    B_tmp = B
+
+    @dataclass
+    class B(PlutusData):
+        AUTO_ID = True
+        a: bytes
+        b: bytes
+
+    assert (
+        B_tmp.CONSTR_ID != B.CONSTR_ID
+    ), "Different classes (different field types) have same default constructor ID"
+
+
+def test_deterministic_constr_ids_local():
+    @dataclass
+    class A(PlutusData):
+        AUTO_ID = True
+        a: int
+        b: bytes
+
+    A_tmp = A
+
+    @dataclass
+    class A(PlutusData):
+        AUTO_ID = True
+        a: int
+        b: bytes
+
+    assert (
+        A_tmp.CONSTR_ID == A.CONSTR_ID
+    ), "Same class has different default constructor ID"
+
+
+def test_deterministic_constr_ids_global():
+    code = """
+from dataclasses import dataclass
+from pycardano import PlutusData
+
+@dataclass
+class A(PlutusData):
+    AUTO_ID = True
+    a: int
+    b: bytes
+
+print(A.CONSTR_ID)
+"""
+    tmpfile = tempfile.TemporaryFile()
+    tmpfile.write(code.encode("utf8"))
+    tmpfile.seek(0)
+    res = subprocess.run([sys.executable], stdin=tmpfile, capture_output=True).stdout
+    tmpfile.seek(0)
+    res2 = subprocess.run([sys.executable], stdin=tmpfile, capture_output=True).stdout
+
+    assert (
+        res == res2
+    ), "Same class has different default constructor id in two consecutive runs"

test/pycardano/test_util.py

@@ -1,7 +1,7 @@
 from test.pycardano.util import chain_context
 
 from pycardano.hash import SCRIPT_HASH_SIZE, ScriptDataHash
-from pycardano.plutus import ExecutionUnits, PlutusData, Redeemer, RedeemerTag
+from pycardano.plutus import ExecutionUnits, PlutusData, Redeemer, RedeemerTag, Unit
 from pycardano.transaction import Value
 from pycardano.utils import min_lovelace_pre_alonzo, script_data_hash
 
@@ -145,7 +145,7 @@ def test_min_lovelace_multi_asset_9(self, chain_context):
 
 
 def test_script_data_hash():
-    unit = PlutusData()
+    unit = Unit()
     redeemers = [Redeemer(unit, ExecutionUnits(1000000, 1000000))]
     redeemers[0].tag = RedeemerTag.SPEND
     assert ScriptDataHash.from_primitive(
@@ -154,14 +154,14 @@ def test_script_data_hash():
 
 
 def test_script_data_hash_datum_only():
-    unit = PlutusData()
+    unit = Unit()
     assert ScriptDataHash.from_primitive(
         "2f50ea2546f8ce020ca45bfcf2abeb02ff18af2283466f888ae489184b3d2d39"
     ) == script_data_hash(redeemers=[], datums=[unit])
 
 
 def test_script_data_hash_redeemer_only():
-    unit = PlutusData()
+    unit = Unit()
     redeemers = []
     assert ScriptDataHash.from_primitive(
         "a88fe2947b8d45d1f8b798e52174202579ecf847b8f17038c7398103df2d27b0"