How to get the balance for a specific account using py-substrate

Question

The following code will return the balance for a few random accounts? How would I pass in a specific account that I am interested in?

url = 'wss://karura.polkawallet.io'
substrate = SubstrateInterface(url)
hash = substrate.get_chain_finalised_head()
result = substrate.query_map('System', 'Account', block_hash = hash, max_results=2)
for account, account_info in result:
     print(f"Free balance of account '{account.value}': {account_info.value['data']['free']}")

The docs mention that you can pass a list in the params argument, but I tried various ways to pass in a list and I can't get it to work. Here is one way I tried:

result = substrate.query_map('System', 'Account', params = ["account=qhYSTHXnF19w3ahxdyxWbrz4kuRm5R5S61RbzFed5LATc86"], block_hash = hash, max_results=2)

Answer 1

The query_map function queries multiple entries of a map.
If you just want a single value, you can use query instead.
Try the following on a local Substrate or Polkadot development node to see how it works:

from substrateinterface import SubstrateInterface


# Connect to a local `polkadot --dev` or `substrate --dev` node.
url = 'ws://127.0.0.1:9944'
substrate = SubstrateInterface(url)

# Alice' development address from https://docs.substrate.io/v3/tools/subkey/#well-known-keys
address = '5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY'

block = substrate.get_chain_finalised_head()
result = substrate.query('System', 'Account', params = [address], block_hash = block)
free = result.value['data']['free']

print(f'Account {address} has {free} planks free balance')

Output:

Account 5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY has 1000000000000000000000 planks free balance