Why can't I send an extrinsic from py-substrate-interface?

Question

Hello guys I am working on submitting an extrinsic via the py-substrate-interface, but for some reason I keep getting an error while following the sample mentioned here. My code is as follows:

    def send_funds(self, destination, amount):
        self.log.info("Sending {} DOT to {} ...".format(amount, destination.strip()))
        substrate = self.create_substrate_instance(self.node_ws_port[0])

        keypair = Keypair.create_from_mnemonic('level payment mom grape proof display cause engage erupt rain hair arm')
        print(keypair)

        call = substrate.compose_call(
            call_module='Balances',
            call_function='transfer',
            call_params={
                'dest': destination,
                'value': ceil(amount * DOT)
            }
        )

        try:
            extrinsic = substrate.create_signed_extrinsic(call=call, keypair=keypair)
        except Exception as e:
            print(e)

        try:
            receipt = substrate.submit_extrinsic(extrinsic, wait_for_inclusion=True)
            self.log.info("Extrinsic '{}' sent and included in block '{}'".format(receipt.extrinsic_hash, receipt.block_hash))
            self.log.info("{} DOT sent to address: {}".format(amount, destination))
        except SubstrateRequestException as e:
            self.log.error("Failed to send: {}".format(e))

I put a try and except block here:

        try:
            extrinsic = substrate.create_signed_extrinsic(call=call, keypair=keypair)
        except Exception as e:
            print(e)

and I get the following error while running this code block:

No more bytes available (offset: 80 / length: 72)

How can I resolve this problem.

ICYMI the Polkascan Technical channel is a good place to ask : https://matrix.to/#/#polkascan:matrix.org — Nuke, Apr 12 '21 at 19:11
great! Would you mind adding the tag `python-substrate` to this question? so others can find it — Nuke, Apr 14 '21 at 02:48

Arjan · Accepted Answer · 2021-04-14T11:29:45.117

Most of the time a RemainingScaleBytesNotEmptyException is raised, it is type registry related. In a Substrate runtime (like Kusama, Polkadot, etc) specific types are defined, which are not (yet) exposed in the metadata, so libraries have to include a decomposition to primitives of those types.

Some pointers for troubleshooting:

The wrong type registry is being used. Most of the time py-substrate-interface can auto-discover which chain its talking to, so only the url have to be specified (https://github.com/polkascan/py-substrate-interface#autodiscover-mode). But with custom runtimes or development properties like type_registry_preset and ss58_format need to be set manually
Because of a recent runtime upgrade the local type registry is out-dated and needs to be updated. This can be achieved by updating the py-scale-codec package, run the substrate.reload_type_registry() function or always use the remote type registries with the use_remote_preset kwarg (See https://github.com/polkascan/py-substrate-interface#keeping-type-registry-presets-up-to-date)
When developing a custom runtime, introduced types can be added in a custom JSON file in the format like https://github.com/polkascan/py-scale-codec/blob/master/scalecodec/type_registry/rococo.json and provided during init (See https://github.com/polkascan/py-substrate-interface#substrate-node-template)

score 1 · Answer 2 · answered Apr 13 '21 at 02:14

OK after digging out a bit more found out that the issue was related to the encoding in parity-scale codec and you need to adjust the network configuration according to your runtime. So I changed from:

    def create_substrate_instance(self, wsport):
        return SubstrateInterface(
                    url=self.rpc_url + wsport,
                    ss58_format=42,
                    type_registry_preset='kusama',
                )

to:

    def create_substrate_instance(self, wsport):
        return SubstrateInterface(
                    url=self.rpc_url + wsport,
                    ss58_format=42,
                    type_registry_preset='substrate-node-template',
                )

and it worked.

Why can't I send an extrinsic from py-substrate-interface?

2 Answers2