How to convert uint to string?

[tennox]

I can't manage to convert (in the end concat) a uint256 to a string:

_artworkId: uint256 = _tokenId % 6
_artworkString: bytes32 = convert(_artworkId, bytes32)
_artworkStringNoPad: Bytes[1] = slice( _artworkString, 31, 1) # otherwise it's prefixed with 31x "\u0000"
return concat(
    b'https://cloudflare-ipfs.com/ipfs/QmZnbXXXZdW9Cp/', 
    _artworkStringNoPad
)

But in the end it returns: https://cloudflare-ipfs.com/ipfs/QmZnbXXXZdW9Cp/\u0001.png

Or maybe my question is: How to convert a unicode-encoded bytes to string?

[tennox]

Got help in discord:

_artworkId: uint256 = _tokenId % 6
_artworkString: bytes32 = convert(_artworkId + 48, bytes32)
_artworkStringNoPad: Bytes[1] = slice( _artworkString, 31, 1) # otherwise it's prefixed with 31x "\u0000"
return concat(
    b'https://cloudflare-ipfs.com/ipfs/QmZXXXCp/',
    _artworkStringNoPad
)

[tennox]

The question remains - how to convert Bytes array to string?

[conceptstom]

[tennox]

That's offtopic for this question, please post your own

[tennox]

I ended up switching to Solidity...

return string(abi.encodePacked(
    super.tokenURI(tokenId % 6),
    '.json'
))

[OrigamiHead]

I have the same question, did you manage to find a way with vyper?

[fubuloubu]

I believe this should work:

baseURI: public(String[56])  # e.g. ipfs://zb2rhe5P4gXftAwvA4eXQ5HJwsER2owDyS9sKaQRRVQPn93bA

# ...

@pure                                            
@internal                                                         
def _digitToString(digit: uint256) -> String[1]:
    assert digit < 10  # only works with digits 0-9                           
    digit_bytes32: bytes32 = convert(digit + 48, bytes32)  # ASCII `0` is 0x30 (48 in decimal)
    digit_bytes1: Bytes[1] = slice(digit_bytes32, 31, 1)  # Remove padding bytes
    return convert(digit_bytes1, String[1])                                                   
                                                                                
                                           
@view             
@internal                                     
def _tokenIdToString(tokenId: uint256) -> String[4]:
    # NOTE: Only handles up to 4 digits, e.g. tokenId in [0, 9999]
    digit1: uint256 = tokenId % 10                  
    digit2: uint256 = (tokenId % 100) / 10                        
    digit3: uint256 = (tokenId % 1000) / 100
    digit4: uint256 = tokenId / 1000               
                                                        
    return concat(                                              
        self._digitToString(digit1),
        self._digitToString(digit2),                   
        self._digitToString(digit3),
        self._digitToString(digit4),
    )                               
                                                                                                  
                                                   
@view                                    
@external                                                                                      
def tokenURI(tokenId: uint256) -> String[66]:                                                       
    return concat(self.baseURI, "/", self._tokenIdToString(tokenId), ".json")  

[fubuloubu]

Note that the algorithm for converting numbers to strings is entirely non-trivial, and depends very much on the expected number of digits. The maximum number of digits that a uint256 can be is 78, so you'd have to do 78 iterations of the above algorithm to handle the arbitrary case (meaning the strings would have to be a minimum of 78 chars in length in ASCII)

[fubuloubu]

Also note that this will produce strings that are 0-padded e.g. 0000, 0001, 0002, ... 9999

[OrigamiHead]

This is great! Thanks for this approach!

[fubuloubu]

As of v0.3.6, we have uint2str!