contract abi not working if json format

Question

Using python 3.11.4, web3 6.9.0

I am using a reduced ERC20 token abi to be able to get decimal & symbol information. Abi is:

ERC20_ABI = [
    {
        "inputs": [],
        "name": "decimals",
        "outputs": [{"internalType": "uint8", "name": "", "type": "uint8"}],
        "stateMutability": "view",
        "type": "function",
        "constant": True
    },
    {
        "inputs": [],
        "name": "symbol",
        "outputs": [{"internalType": "string", "name": "", "type": "string"}],
        "stateMutability": "view",
        "type": "function",
        "constant": True
    }
]

W/ this, code works as expected. However, if I wrap the ABI definition in triple quotes:

ERC20_ABI = """[
    {
        "inputs": [],
        "name": "decimals",
        "outputs": [{"internalType": "uint8", "name": "", "type": "uint8"}],
        "stateMutability": "view",
        "type": "function",
        "constant": True
    },
    {
        "inputs": [],
        "name": "symbol",
        "outputs": [{"internalType": "string", "name": "", "type": "string"}],
        "stateMutability": "view",
        "type": "function",
        "constant": True
    }
]"""

Then I get the following error:

apply_formatters_to_dict
    raise ValueError(new_error_message) from exc
ValueError: Could not format invalid value '[\n    {\n\t\t"inputs": [],\n        "name": "decimals",\n        "outputs": [{"internalType": "uint8", "name": "", "type": "uint8"}],\n        "stateMutability": "view",\n        "type": "function",\n        "constant": True\n    },\n    {\n        "inputs": [],\n        "name": "symbol",\n        "outputs": [{"internalType": "string", "name": "", "type": "string"}],\n        "stateMutability": "view",\n        "type": "function",\n        "constant": True\n    }\n]' as field 'abi'

Does anyone know why this ABI cannot be in JSON format? Not vital that it must be but I am curious why web3 is having trouble decoding it...

Answer 1

Triple quotes turn your ABI into a string instead of a dictionary. If you want to go the string route, you need to turn the string back into a data structure with something like json.loads (that will parse your JSON)/.

For example:

import json

ERC20_ABI = """[
    {
        "inputs": [],
        "name": "decimals",
        "outputs": [{"internalType": "uint8", "name": "", "type": "uint8"}],
        "stateMutability": "view",
        "type": "function",
        "constant": True
    },
    {
        "inputs": [],
        "name": "symbol",
        "outputs": [{"internalType": "string", "name": "", "type": "string"}],
        "stateMutability": "view",
        "type": "function",
        "constant": True
    }
]"""

ERC20_ABI = json.loads(ERC20_ABI)

Answer 2

Turns out it was capitalizing the Booleans! If using json strings need to change "constant": True to "constant": true