0x-contract-wrappers & 0x/abi-gen: TypeError: Cannot instantiate typing.Union

[damjankuznar]

Expected Behavior

No TypeError should be raised when calling EncodeErc1155AssetDataMethod.call() or DevUtils.encode_erc1155_asset_data.call().

Current Behavior

Currently the following error occurs when calling the above mentioned method:

  File "/home/.../.../.../.../venv/lib/python3.7/site-packages/zero_ex/contract_wrappers/dev_utils/__init__.py", line 1530, in call
    return Union[bytes, str](returned)
  File "/usr/lib/python3.7/typing.py", line 678, in __call__
    result = self.__origin__(*args, **kwargs)
  File "/usr/lib/python3.7/typing.py", line 332, in __call__
    raise TypeError(f"Cannot instantiate {self!r}")
TypeError: Cannot instantiate typing.Union

The problems seems to be with @0x/abi-gen which does not generate a valid Python code, basically instantiating type hint class:

from typing import Union
# ...
class EncodeErc1155AssetDataMethod(ContractMethod):
    # ...
    def call(...):
        # ...
        return Union[bytes, str](returned)

Possible Solution

Steps to Reproduce (for bugs)

from web3 import Web3
from zero_ex.contract_addresses import chain_to_addresses, ChainId
from zero_ex.contract_wrappers.dev_utils import DevUtils
w3 = Web3.HTTPProvider(endpoint_uri="http://127.0.0.1:8545")
contract_addresses = chain_to_addresses(ChainId.MAINNET)
dev_utils = DevUtils(web3_or_provider=w3, contract_address=contract_addresses.dev_utils)
result = dev_utils.encode_erc1155_asset_data.call(
    "0xc1f4b0eea2bd6690930e6c66efd3e197d620b9c2", [2056], [1], "0x"
)
# this should result in the following error:
Traceback (most recent call last):
  File "/home/.../.../.../.../venv/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 3319, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-3-e419739043d5>", line 8, in <module>
    "0xc1f4b0eea2bd6690930e6c66efd3e197d620b9c2", [2056], [1], "0x"
  File "/home/.../.../.../.../venv/lib/python3.7/site-packages/zero_ex/contract_wrappers/dev_utils/__init__.py", line 1530, in call
    return Union[bytes, str](returned)
  File "/usr/lib/python3.7/typing.py", line 678, in __call__
    result = self.__origin__(*args, **kwargs)
  File "/usr/lib/python3.7/typing.py", line 332, in __call__
    raise TypeError(f"Cannot instantiate {self!r}")
TypeError: Cannot instantiate typing.Union

Context

Construct the order data for listing

Your Environment

$ pip show 0x-contract-wrappers 
Name: 0x-contract-wrappers
Version: 2.0.0
Summary: Python wrappers for 0x smart contracts
Home-page: https://github.com/0xproject/0x-monorepo/tree/development/python-packages/contract_wrappers
Author: F. Eugene Aumson
Author-email: feuGeneA@users.noreply.github.com
License: Apache 2.0
Location: /home/.../.../.../.../venv/lib/python3.7/site-packages
Requires: 0x-order-utils, web3, attrs, 0x-contract-addresses, 0x-json-schemas, eth-utils, mypy-extensions, 0x-contract-artifacts
Required-by: 

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[stale[bot]]

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