Howto Monitor the blockchain for certain operations

Block Structure

A block takes the following form:

{'extensions': [],
 'previous': '000583428a021b14c02f0faaff12a4c686e475e3',
 'timestamp': '2017-04-21T08:38:35',
 'transaction_merkle_root': '328be3287f89aa4d21c69cb617c4fcc372465493',
 'transactions': [{'expiration': '2017-04-21T08:39:03',
                   'extensions': [],
                   'operation_results': [[0, {}]],
                   'operations': [
                           {'amount': {'amount': 100000,
                                       'asset_id': '1.3.0'},
                            'extensions': [],
                            'fee': {'amount': 2089843,
                                    'asset_id': '1.3.0'},
                            'from': '1.2.18',
                            'memo': {'from': 'PPY1894jUspGi6fZwnUmaeCPDZpke6m4T9bHtKrd966M7qYz665xjr',
                                     'message': '5d09c06c4794f9bcdef9d269774209be',
                                     'nonce': '7364013452905740719',
                                     'to': 'PPY16MRyAjQq8ud7hVNYcfnVPJqcVpscN5So8BhtHuGYqET5GDW5CV'},
                            'to': '1.2.6'}]
                   'ref_block_num': 33602,
                   'ref_block_prefix': 337314442,
                   'signatures': ['1f3755deaa7f9........']}],
 'witness': '1.6.4',
 'witness_signature': '2052571f091c4542...........'}

Please note that a block can carry multiple transactions while each transaction carries multiple operations. Each operation could be a transfer, or any other type of operation from a list of available operations. Technically, an operation could be seen as a smart contract that comes with operation-specific side-information and results in some changes in the blockchain database.

In the example above, the operation type is identified by the 0, which makes it a transfer and the structure afterwards carries the transfer-specific side information, e.g. from, to accounts, fee aswell as the memo.

Polling Approach

Blocks can be polled with as little code as this:

from peerplays.blockchain import Blockchain
chain = Blockchain()
for block in chain.blocks(start=START_BLOCK):


chain.blocks() is a blocking call that will wait for new blocks and yield them to the for loop when they arrive.

Alternatively, one can construct a loop that only yields the operations on the blockchain and does not show the block structure:

from peerplays.blockchain import Blockchain
chain = Blockchain()
for op in chain.ops(start=START_BLOCK):  # Note the `ops`

If you are only interested in transfers, you may want to use this instead:

from peerplays.blockchain import Blockchain
chain = Blockchain()
for transfer in["transfer"], start=START_BLOCK):  # Note the `ops`


By default, the Blockchain() instance will only look at irrversible blocks, this means that blocks are only considered if they are approved/signed by a majority of the witnesses and this lacks behind the head block by a short period of time (in the seconds to low minutes).

Notification Approach

under construction