Solidity and Ethereum int256 for Python, SQLAlchemy and SQL Databases, efficiently as 32 bytes blobs

example.py

class LiquidityChanged(TransactionEvent):
    """A sampled liquidity at any moment."""
    __tablename__ = "liquidity"
    delta0 = sa.Column(Int257, nullable=False, index=False)

tests.py

from utils import Int257


def test_max_positive():
    max_positive = int(2**256 - 1)
    int257 = Int257()
    bin = int257.process_bind_param(max_positive, None)
    assert bin == b'\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff'
    i = int257.process_result_value(bin, None)
    assert i == max_positive


def test_max_negative():
    max_negative = -int(2**256 - 1)
    int257 = Int257()
    bin = int257.process_bind_param(max_negative, None)
    assert bin == b'\x01\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff'
    i = int257.process_result_value(bin, None)
    assert i == max_negative

utils.py

from sqlalchemy import types


class Int257(types.TypeDecorator):
    """SQLAlchemy class to store Ethereum Virtual Machine (EVM) uint256s in an SQL database.

    Unlike Solidity's native uin256, this is one allows to store the sign and negative numbers,
    making it more useful for accounting data.

    Should be a bit more efficient than storing stringified decimals in a database.
    """

    # uint256 is 32 bytes
    impl = types.BINARY(33)

    MAX_UINT256 = 2**256

    BYTE_ORDER = "big"

    def load_dialect_impl(self, dialect):
        return dialect.type_descriptor(types.BINARY(33))

    def process_bind_param(self, val: int, dialect):
        assert type(val) == int
        assert val < Int257.MAX_UINT256
        # Separate sign and 256-bit int body
        # The sign is stored as the highest 33th byte
        b = abs(val).to_bytes(32, byteorder=Int257.BYTE_ORDER)
        sign = b"\0" if val >= 0 else b"\1"
        return sign + b

    def process_result_value(self, val: bytes, dialect):
        assert type(val) == bytes
        sign = -1 if val[0] else 1
        lower = val[1:]
        number = int.from_bytes(lower, byteorder=Int257.BYTE_ORDER)
        return sign * number