Parse Ogmios protocol ratios instead of evaluating them

pycardano/backend/ogmios_v6.py

@@ -162,18 +162,26 @@ def _fetch_protocol_param(self) -> ProtocolParameters:
                 ),
                 key_deposit=protocol_parameters.stake_credential_deposit.lovelace,
                 pool_deposit=protocol_parameters.stake_pool_deposit.lovelace,
-                pool_influence=eval(protocol_parameters.stake_pool_pledge_influence),
-                monetary_expansion=eval(protocol_parameters.monetary_expansion),
-                treasury_expansion=eval(protocol_parameters.treasury_expansion),
+                pool_influence=self._fraction_parser(
+                    protocol_parameters.stake_pool_pledge_influence
+                ),
+                monetary_expansion=self._fraction_parser(
+                    protocol_parameters.monetary_expansion
+                ),
+                treasury_expansion=self._fraction_parser(
+                    protocol_parameters.treasury_expansion
+                ),
                 decentralization_param=None,  # type: ignore[arg-type]
                 extra_entropy=protocol_parameters.extra_entropy,
                 protocol_major_version=protocol_parameters.version.get("major"),
                 protocol_minor_version=protocol_parameters.version.get("minor"),
                 min_utxo=None,  # type: ignore[arg-type]
-                price_mem=eval(
+                price_mem=self._fraction_parser(
                     protocol_parameters.script_execution_prices.get("memory")
                 ),
-                price_step=eval(protocol_parameters.script_execution_prices.get("cpu")),
+                price_step=self._fraction_parser(
+                    protocol_parameters.script_execution_prices.get("cpu")
+                ),
                 max_tx_ex_mem=protocol_parameters.max_execution_units_per_transaction.get(
                     "memory"
                 ),

test/pycardano/backend/test_ogmios_v6_ratio.py

@@ -0,0 +1,56 @@
+from types import SimpleNamespace
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from pycardano.backend.ogmios_v6 import OgmiosV6ChainContext
+
+
+def _ogmios_params(**overrides):
+    params = dict(
+        min_fee_constant=SimpleNamespace(lovelace=155381),
+        min_fee_coefficient=44,
+        min_stake_pool_cost=SimpleNamespace(lovelace=0),
+        max_block_body_size={"bytes": 65536},
+        max_transaction_size={"bytes": 16384},
+        max_block_header_size={"bytes": 1100},
+        stake_credential_deposit=SimpleNamespace(lovelace=0),
+        stake_pool_deposit=SimpleNamespace(lovelace=0),
+        stake_pool_pledge_influence="1/10",
+        monetary_expansion="1/10",
+        treasury_expansion="1/10",
+        extra_entropy="neutral",
+        version={"major": 9, "minor": 0},
+        script_execution_prices={"memory": "721/10000000", "cpu": "577/10000"},
+        max_execution_units_per_transaction={"memory": 1, "cpu": 1},
+        max_execution_units_per_block={"memory": 1, "cpu": 1},
+        max_value_size={"bytes": 4000},
+        collateral_percentage=150,
+        max_collateral_inputs=3,
+        min_utxo_deposit_coefficient=4310,
+        plutus_cost_models={},
+        max_ref_script_size={"bytes": 200000},
+        min_fee_ref_scripts=None,
+    )
+    params.update(overrides)
+    return SimpleNamespace(**params)
+
+
+def _fetch(params):
+    ctx = OgmiosV6ChainContext()
+    client = MagicMock()
+    client.query_protocol_parameters.execute.return_value = (params, None)
+    client.__enter__.return_value = client
+    with patch("pycardano.backend.ogmios_v6.OgmiosClient", return_value=client):
+        return ctx._fetch_protocol_param()
+
+
+def test_protocol_ratio_rejects_a_python_expression():
+    with pytest.raises(ValueError):
+        _fetch(_ogmios_params(monetary_expansion="1+1"))
+
+
+def test_protocol_ratio_parses_a_fraction():
+    parsed = _fetch(_ogmios_params())
+    assert parsed.monetary_expansion == 0.1
+    assert parsed.price_mem == 721 / 10000000