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Creating a Data Source

In this section, we will take a look at how to create a data source.

Writing the data source​

In order for the data source to run, always make sure to add a shebang line containing #!/usr/bin/env python3 and to print the function output. A simple Hello World! example can be seen below.

#!/usr/bin/env python3

import sys


def main():
    return "Hello World!"


if __name__ == "__main__":
    try:
        print(main())
    except Exception as e:
        print(str(e), file=sys.stderr)
        sys.exit(1)

More Examples​

However, in order to better understand the structure and implementation of a data source, let’s look at two more examples below: Gold Price and Token Total Supply.

Gold Price​

First, let’s look at a data source that queries GoldPrice.org for the current price of gold. The script itself is written in Python and although this specific data source does not expect any arguments, a data source can have any number of arguments required.

#!/usr/bin/env python3

import requests
import sys


URL = "https://data-asg.goldprice.org/dbXRates/USD"
HEADERS = {'User-Agent': 'curl/7.64.1'}

def main():
    try:
        pxs = requests.get(URL, headers=HEADERS).json()
        return pxs['items'][0]['xauPrice']
    except Exception as e:
        raise e

if __name__ == "__main__":
    try:
        print('{0:.2f}'.format(main()))
    except Exception as e:
        print(str(e), file=sys.stderr)
        sys.exit(1)

Token Total Supply​

As mentioned above, a data source can take any number of arguments. The example below, gives an example of a data source which requires two arguments. The data source shown below queries the given network's RPC endpoint for the total supply of a given token address.

#!/usr/bin/env python3

import requests
import sys


def main(rpc, to):
    headers = {
        "Content-Type": "application/json",
    }
    data = (
        """{ "jsonrpc": "2.0", "method": "eth_call", "params": [ { "to": "%s", "data": "0x18160ddd" }, "latest" ], "id": 1 }"""
        % (to)
    )
    response = requests.post(
        rpc,
        headers=headers,
        data=data,
    )
    return int(response.json()["result"], 16)


if __name__ == "__main__":
    try:
        print(main(sys.argv[1], sys.argv[2]))
    except Exception as e:
        print(str(e), file=sys.stderr)
        sys.exit(1)

More examples​

For more data source examples, please refer to the ones available on our Mainnet to get an idea of the different types of data source used on BandChain: