polymath-substrate-interface 0.3.1

Library for interfacing with a Polymesh node

Python Substrate Interface

Python Substrate Interface Library

Description

This library specializes in interfacing with a Substrate node, providing additional convenience methods to deal with SCALE encoding/decoding (the default output and input format of the Substrate JSONRPC), metadata parsing, type registry management and versioning of types.

Documentation

https://polkascan.github.io/py-substrate-interface/

Installation

pip install substrate-interface

Examples

Simple example, initialize interface and get head block hash of Kusama chain:

Initialization

substrate = SubstrateInterface(
    url="wss://kusama-rpc.polkadot.io/",
    address_type=2,
    type_registry_preset='kusama'
)

substrate.get_chain_head() 

Note on support for wss, this is still quite limited at the moment as connections are not reused yet. Until support is improved it is prefered to use http endpoints (e.g. http://127.0.0.1:9933)

Get extrinsics for a certain block

# Set block_hash to None for chaintip
block_hash = "0x588930468212316d8a75ede0bec0bc949451c164e2cea07ccfc425f497b077b7"

# Retrieve extrinsics in block
result = substrate.get_runtime_block(block_hash=block_hash)

for extrinsic in result['block']['extrinsics']:

    if 'account_id' in extrinsic:
        signed_by_address = ss58_encode(address=extrinsic['account_id'], address_type=2)
    else:
        signed_by_address = None

    print('\nModule: {}\nCall: {}\nSigned by: {}'.format(
        extrinsic['call_module'],
        extrinsic['call_function'],
        signed_by_address
    ))

    # Loop through params
    for param in extrinsic['params']:

        if param['type'] == 'Address':
            param['value'] = ss58_encode(address=param['value'], address_type=2)

        if param['type'] == 'Compact<Balance>':
            param['value'] = '{} DOT'.format(param['value'] / 10**12)

        print("Param '{}': {}".format(param['name'], param['value']))

Make a storage call

The modules and storage functions are provided in the metadata (see substrate.get_metadata_storage_functions()), parameters will be automatically converted to SCALE-bytes (also including decoding of SS58 addresses).

print("\n\nCurrent balance: {} DOT".format(
    substrate.get_runtime_state(
        module='Balances',
        storage_function='FreeBalance',
        params=['EaG2CRhJWPb7qmdcJvy3LiWdh26Jreu9Dx6R1rXxPmYXoDk']
    ).get('result') / 10**12
))

Or get a historic balance at a certain block hash:

print("Balance @ {}: {} DOT".format(
    block_hash, 
    substrate.get_runtime_state(
        module='Balances',
        storage_function='FreeBalance',
        params=['EaG2CRhJWPb7qmdcJvy3LiWdh26Jreu9Dx6R1rXxPmYXoDk'],
        block_hash=block_hash
    ).get('result') / 10**12
))

Compose call

Py-substrate-interface will also let you compose calls you can use as an unsigned extrinsic or as a proposal:

payload = substrate.compose_call(
    call_module='Balances',
    call_function='transfer',
    call_params={
        'dest': 'EaG2CRhJWPb7qmdcJvy3LiWdh26Jreu9Dx6R1rXxPmYXoDk',
        'value': 1000000000000
    }
)

Py-substrate-interface makes it also possible to easily interprete changed types and historic runtimes. As an example we create an (not very useful) historic call of a module that has been removed later on: retrieval of historic metadata and apply the correct version of types in the type registry is all done automatically. Because parsing of metadata and type registry is quite heavy, the result will be cached per runtime id. In the future there could be support for caching backends like Redis to make this cache more persistent.

Create an unsigned extrinsic of a module that was removed by providing block hash:

payload = substrate.compose_call(
    call_module='Nicks',
    call_function='clear_name',
    call_params={},
    block_hash="0x918107632d7994d50f3661db3af353d2aa378f696e47a393bab573f63f7d6c3a"
)

License

https://github.com/polkascan/py-substrate-interface/blob/master/LICENSE