Vyper | Firmware of Anycubic 3D printer Vyper | 3D Printing library

I finally managed to solve this. I figured out that the error was due to vyper, as vyper --version also gave a similar error. So, I went to the last exception raised:

The approval mechanism is described in more depth in the ERC-721 standard.

What is the mechanic of approve in it?

A token owner can approve another address (an operator) to spend a specific token using the approve() function, as well as all of the owner's tokens using setApprovalForAll().

What is isApprovedForAll does?

It's a getter function returning bool value whether an operator address can spend all of the owner tokens (i.e. they have been approved using the setApprovalForAll() function) - or not.

I don't need to use approve method. I just use transferFrom() is enough.

Correct if you're only spending your own tokens.

If you want another address to spend your tokens, or if you want to spend tokens belonging to another owner (possibly one of your other addresses), you'll need to use the approval mechanism.

I did refactor your code, for improve it. And fixed issues you wanted to solve.

You can use the overrides parameter. It's used after all contract function arguments.

In your case, the contract function has 0 arguments so the overrides is on position 1.

Look at the description of range-function, there just one way to pass a variable to it:

If send() target address is a smart contract it will execute the fallback function.

If the currentLeader points to a smart contract that has a fallback function that has been intentionally made to revert on failed send, the bid() won't work for any participants until currentLeader has been changed.

More information here.

This is not a "DoS" attack but simply gotcha in Solidity programming.