Unable decode the event

[99Kies]

from substrateinterface import SubstrateInterface, Keypair
from scalecodec import ScaleBytes

substrate=SubstrateInterface(url='ws://127.0.0.1:9944',type_registry_preset='default')
event_data = "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"
metadata = substrate.get_block_metadata()

system_pallet = [p for p in metadata.pallets if p['name'] == 'System'][0]
event_storage_function = [s for s in system_pallet['storage']['entries'] if s['name'] == "Events"][0]


event = substrate.runtime_config.create_scale_object(
    event_storage_function.get_value_type_string(), data=ScaleBytes(event_data), metadata=metadata
)
print(event)
print(event.decode())

return message:

None
Traceback (most recent call last):
  File "c:\Users\lizhaoyang\Desktop\demo.py", line 711, in <module>
    print(event.decode())
  File "C:\Users\lizhaoyang\AppData\Local\Programs\Python\Python39\lib\site-packages\scalecodec\base.py", line 666, in decode
    self.value_serialized = self.process()
  File "C:\Users\lizhaoyang\AppData\Local\Programs\Python\Python39\lib\site-packages\scalecodec\types.py", line 792, in process
    element = self.process_type(self.sub_type, metadata=self.metadata)
  File "C:\Users\lizhaoyang\AppData\Local\Programs\Python\Python39\lib\site-packages\scalecodec\base.py", line 749, in process_type
    obj.decode(check_remaining=False)
  File "C:\Users\lizhaoyang\AppData\Local\Programs\Python\Python39\lib\site-packages\scalecodec\base.py", line 666, in decode
    self.value_serialized = self.process()
  File "C:\Users\lizhaoyang\AppData\Local\Programs\Python\Python39\lib\site-packages\scalecodec\types.py", line 2545, in process
    self.phase = self.process_type('Phase')
  File "C:\Users\lizhaoyang\AppData\Local\Programs\Python\Python39\lib\site-packages\scalecodec\base.py", line 748, in process_type
    obj = self.runtime_config.create_scale_object(type_string, self.data, **kwargs)
  File "C:\Users\lizhaoyang\AppData\Local\Programs\Python\Python39\lib\site-packages\scalecodec\base.py", line 160, in create_scale_object
    raise NotImplementedError('Decoder class for "{}" not found'.format(type_string))
NotImplementedError: Decoder class for "Phase" not found

[arjanz]

The best (and easiest) way to read a storage function in substrateinterface is to use the query() function:

event = substrate.query("System", "Events", block_hash="0x1029553d55f2aa71b164add49282ce56f643bf4ba422cb98278a2e4f32f7c8b4")

But if you for some reason still need to manually decode a SCALE object, you will need to initialize the runtime (to add the type definitions from the metadata to the registry of the library).

You can simply do this by added:

substrate.init_runtime()
event = substrate.runtime_config.create_scale_object(
    event_storage_function.get_value_type_string(), data=ScaleBytes(event_data), metadata=metadata
)

But I see there is a need for a convenience function, so I will add create_scale_object() for SubstrateInterface that will do this automatically for you.

[arjanz]

There is in fact already a convenience method, check out: https://polkascan.github.io/py-substrate-interface/#substrateinterface.SubstrateInterface.decode_scale

[99Kies]

thanks!

I have encountered a new error here, but I can't track the information. Do you have similar problems?

  /usr/local/lib/python3.9/dist-packages/scalecodec/base.py:732: DeprecationWarning: Use RuntimeConfigurationObject.create_scale_object() instead
    warnings.warn("Use RuntimeConfigurationObject.create_scale_object() instead", DeprecationWarning)

[99Kies]

and about ScaleDecoder.get_decoder_class. How should I use it correctly?

[99Kies]

thanks!

I have encountered a new error here, but I can't track the information. Do you have similar problems?

  /usr/local/lib/python3.9/dist-packages/scalecodec/base.py:732: DeprecationWarning: Use RuntimeConfigurationObject.create_scale_object() instead
    warnings.warn("Use RuntimeConfigurationObject.create_scale_object() instead", DeprecationWarning)

https://github.com/polkascan/py-scale-codec/blob/master/scalecodec/base.py#L732
Why need this output here?

[arjanz]

@99Kies

I have encountered a new error here, but I can't track the information. Do you have similar problems?

Well I added that notice myself, so I am familiar :) Because all SCALE classes and creation of SCALE objects should run via the RuntimeConfigurationObject, because the ScaleDecoder base class is too global and not context aware.

So see https://github.com/polkascan/py-scale-codec#multiple-runtime-configurations

And an example from the SubstrateInterface perspective:

metadata_decoder = substrate.runtime_config.create_scale_object(
            'MetadataVersioned', ScaleBytes(metadata_node_template_hex)
        )
        metadata_decoder.decode()

[arjanz]

https://github.com/polkascan/py-scale-codec/blob/master/scalecodec/base.py#L732
Why need this output here?

Because in future releases this function will be removed, this is a transition stage

[99Kies]

Thanks!