markets "contractSize" wrong data type

• OS: linux
• Programming Language version: all (although i personally only really care about python for now)
• CCXT version: latest main - v1.65.19

the type of contractSize seems to be a string throughout the exchanges I’ve tested - which seems and feels wrong to me.

Based on the documentation i’d expect it to be a float, which would align the “position structure” with the response of the market response.

I also don’t think any value other than a float will be a possible/allowed value for contractSize - as we’d expect to multiply (or divide) by that number to go from amount to what the exchange expects and viceversa.

Having this as string makes all calculations necessary for futures quite odd, as we’ll have to do explicitly convert contract-size to number (e.g. amount * float(market['contractSize'])).

 node examples/js/cli.js okex market BTC/USDT:USDT

okex.market (BTC/USDT:USDT)
0 ms
{         limits: { leverage: { min: undefined, max: 125 },
                      amount: { min: 1, max: undefined },
                       price: { min: 0.1, max: undefined },
                        cost: { min: 0.1, max: undefined }  },
       precision: { amount: 1, price: 0.1 },
       tierBased:    undefined,
      percentage:    undefined,
           taker:    0.0005,
           maker:    0.0002,
              id:   "BTC-USDT-SWAP",
          symbol:   "BTC/USDT:USDT",
            base:   "BTC",
           quote:   "USDT",
          baseId:   "BTC",
         quoteId:   "USDT",
        settleId:   "USDT",
          settle:   "USDT",
            info: {     alias: "",
                      baseCcy: "",
                     category: "1",
                       ctMult: "1",
                       ctType: "linear",
                        ctVal: "0.01",
                     ctValCcy: "BTC",
                      expTime: "",
                       instId: "BTC-USDT-SWAP",
                     instType: "SWAP",
                        lever: "125",
                     listTime: "1636620057000",
                        lotSz: "1",
                        minSz: "1",
                      optType: "",
                     quoteCcy: "",
                    settleCcy: "USDT",
                        state: "live",
                          stk: "",
                       tickSz: "0.1",
                          uly: "BTC-USDT"       },
            type:   "swap",
            spot:    false,
         futures:    false,
            swap:    true,
        contract:    true,
          option:    false,
          linear:    true,
         inverse:    false,
          active:    true,
    contractSize:   "0.01",    <-- would like to be a number ... 
          expiry:    undefined,
  expiryDatetime:    undefined                               

[frosty00]

Yeah I think probably we’ll need to have a variable called contractSizeString or similar

[samgermain]

@xmatthias it may seem like it is the wrong data type but we actually store it as a string on purpose since we need to do stringMaths using contractSize inside of parsePosition and some other places

Having this as string makes all calculations necessary for futures quite odd, as we’ll have to do explicitly convert contract-size to number (e.g. amount * float(market[‘contractSize’])).

that’s cause you are using floating point maths

Based on the documentation i’d expect it to be a float, which would align the “position structure” with the response of the market response.

I’ll update the docs

I think that we should convert contractSize to a string when we need to do string math internally, but the value returned from fetchMarkets should be a float. Almost every user would want the contract size to be a float, and would expect it to be a float, and returning a string is just kind of weird to the user when it’s only a string to help with internal use