Well, you piqued my interest!

This got me to install Python 3 and, using PIP to add the requests repository.

After all that I thought I would contribute by adding a total...

Altered the code as follows:

import json, requests

splinterlands_accounts = ["account1", "account2", "account3"]

print("----------------------------------")
print("Account               DEC Total")
print("----------------------------------")

totalDEC = float("0")

for account in splinterlands_accounts:

    url = "https://api2.splinterlands.com/players/balances?username=" + account
    spldata = json.loads(requests.get(url).text)

    for data in spldata:
        if data["token"] == "DEC":
            spaces = " " * (20-len(data['player']))
            print("{} {} {}".format(data['player'], spaces, data['balance']))
            totalDEC = totalDEC + float(data['balance'])

print("----------------------------------")
spaces = " " * (18-len(str(totalDEC)))
print("{} {} {}".format("Total DEC", spaces, str(totalDEC)))
print("----------------------------------")