PALChain loading fails

[liangz1]

System Info

langchain==0.0.176

Who can help?

@hwchase17

Information

• The official example notebooks/scripts
• My own modified scripts

Related Components

• LLMs/Chat Models
• Embedding Models
• Prompts / Prompt Templates / Prompt Selectors
• Output Parsers
• Document Loaders
• Vector Stores / Retrievers
• Memory
• Agents / Agent Executors
• Tools / Toolkits
• Chains
• Callbacks/Tracing
• Async

Reproduction

from langchain.chains import PALChain
from langchain import OpenAI

llm = OpenAI(temperature=0, max_tokens=512)
pal_chain = PALChain.from_math_prompt(llm, verbose=True)
question = "Jan has three times the number of pets as Marcia. Marcia has two more pets than Cindy. If Cindy has four pets, how many total pets do the three have?"
pal_chain.save("/Users/liang.zhang/pal_chain.yaml")
loaded_chain = load_chain("/Users/liang.zhang/pal_chain.yaml")

Error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Input In [17], in <cell line: 1>()
----> 1 loaded_chain = load_chain("/Users/liang.zhang/pal_chain.yaml")

File ~/miniforge3/envs/mlflow-3.8/lib/python3.8/site-packages/langchain/chains/loading.py:449, in load_chain(path, **kwargs)
    447     return hub_result
    448 else:
--> 449     return _load_chain_from_file(path, **kwargs)

File ~/miniforge3/envs/mlflow-3.8/lib/python3.8/site-packages/langchain/chains/loading.py:476, in _load_chain_from_file(file, **kwargs)
    473     config["memory"] = kwargs.pop("memory")
    475 # Load the chain from the config now.
--> 476 return load_chain_from_config(config, **kwargs)

File ~/miniforge3/envs/mlflow-3.8/lib/python3.8/site-packages/langchain/chains/loading.py:439, in load_chain_from_config(config, **kwargs)
    436     raise ValueError(f"Loading {config_type} chain not supported")
    438 chain_loader = type_to_loader_dict[config_type]
--> 439 return chain_loader(config, **kwargs)

File ~/miniforge3/envs/mlflow-3.8/lib/python3.8/site-packages/langchain/chains/loading.py:234, in _load_pal_chain(config, **kwargs)
    232 if "llm" in config:
    233     llm_config = config.pop("llm")
--> 234     llm = load_llm_from_config(llm_config)
    235 elif "llm_path" in config:
    236     llm = load_llm(config.pop("llm_path"))

File ~/miniforge3/envs/mlflow-3.8/lib/python3.8/site-packages/langchain/llms/loading.py:14, in load_llm_from_config(config)
     12 def load_llm_from_config(config: dict) -> BaseLLM:
     13     """Load LLM from Config Dict."""
---> 14     if "_type" not in config:
     15         raise ValueError("Must specify an LLM Type in config")
     16     config_type = config.pop("_type")

TypeError: argument of type 'NoneType' is not iterable

Expected behavior

No errors should occur.