Python substrate-interface discovering which params need to be passed into query function for parallel API?

Question

I am trying to find the correct parameters to pass into the query function for the substrate interface module when interacting with the parallel api to interact with their AMM. I attempted to modify the code from the linked post:

How to determine which parameters are required when using substrate.query() to query a storage_function from polkascan's py-substrate-interface?

Below is my adapted code:

from substrateinterface import SubstrateInterface

paraurl = 'wss://rpc.parallel.fi'

substrate = SubstrateInterface(
    url=paraurl,
)

storage_function = substrate.get_metadata_storage_function('AMM','Pools')

typeString = storage_function.get_params_type_string()
print('Storage Function params length:', len(typeString))


# Retrieve a SCALE object of the param type
param_type = substrate.create_scale_object(storage_function.get_params_type_string()[0])

# Possible options of Enum type
print(param_type.type_mapping)

token_param = substrate.create_scale_object(param_type.type_mapping[0][1])

# Show possible options
print(token_param.type_mapping)

However, I am receiving the error:

  File "/home/travnado300/Documents/Python Scripts/Substrate Interactions/Parallel.py", line 30, in <module>
    token_param = substrate.create_scale_object(param_type.type_mapping[0][1])
  TypeError: 'NoneType' object is not subscriptable

I am wondering if this is just an issue with the parallel API not having all of the information available or if there is a way to access the params needed to pass into the function:

substrate.query()

Answer 1

You can use the storage_function.get_param_info() to get more information about the param types:

storage_function = substrate.get_metadata_storage_function('AMM', 'Pools')

param_info = storage_function.get_param_info()

print(param_info)
# [{'primitive': 'u32'}, {'primitive': 'u32'}]

More information see: https://github.com/polkascan/py-substrate-interface#type-information-about-how-to-format-parameters

Answer 2

I am wondering if you are missing a step here, before using param_type. Possibly a decode() after create_scale_object, similar to https://github.com/polkascan/py-scale-codec/blob/master/README.md#encode-a-call