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I have an identical contract on the Mainnet and Ropsten. Both work fine in Remix. Using a python program on my Windows machine, I find that I get an error accessing the Ropsten contract, but not the mainnet version. All I changed in my Python program was the contract address and provider URL: "https://mainnet.infura.io/v3/3e4616a1aed64da3b29e20c2970e23b7" to "https://ropsten.infura.io/v3/3e4616a1aed64da3b29e20c2970e23b7"

The flawed program generates an error on the first contract call

currDay = contract.functions.currentDay().call()

This generates a scalar output, type uint8. The error I get is:

web3.exceptions.BadFunctionCallOutput: Could not decode contract function call currentDay return data b'' for output_types ['uint8']

As mentioned, this works fine for the mainnet, and also works fine within Remix for both the Ropsten and Mainnet contracts.

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The contract address will be different on different networks. This is why the call fails.

  • As mentioned, I changed the contract address. The contract is identical, just one on Ropsten, one on the Mainnet. I then only changed the contract address and the provider URL to account for the difference. I suppose there's something in the python Web3 or HTTPProvider packages. – Eric Falkenstein Jul 28 '20 at 18:12
  • Looks like I was right :) – Mikko Ohtamaa Jul 29 '20 at 11:07
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My bad: My program pulled in the Mainnet contract address from the json. This overwrote the correct address I posted above it. I forgot I had that address definition buried there, as it's redundant.

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