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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...

2 Answers 2

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)
1
  • web3 internally does this. I have other ABIs in string format that work fine but specifically this one generates an error. I am curious if there is anything specific to this ABI that causes an error in web3's parser.
    – AdamMuzz
    Sep 30, 2023 at 19:28
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Turns out it was capitalizing the Booleans! If using json strings need to change "constant": True to "constant": true

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