plot_metric does not work with Booster

[js850]

plot_metric works with LGBMModel, but not with lightgbm.basic.Booster.

This seems to be by design, but seems like a clear gap in functionality.

https://github.com/microsoft/LightGBM/blob/master/python-package/lightgbm/plotting.py

    if isinstance(booster, LGBMModel):
        eval_results = deepcopy(booster.evals_result_)
    elif isinstance(booster, dict):
        eval_results = deepcopy(booster)
    else:
        raise TypeError('booster must be dict or LGBMModel.')

I'm just getting started with lightgbm, is there an easy workaround?

[js850]

After more hunting I found the workaround from this issue: #1491 which points to this example

This took me a surprisingly long time to figure out. I would suggest updating the exception message from plot_metric to give instructions on how to use the method with Booster

something like

if isinstance(booster, Booster):
    raise Exception("to plot the metrics for a Booster type, first output the metrics using evals_result then pass that in to this method as `booster`")

[shiyu1994]

@js850 Thanks for figuring that out. Good suggestion to make usage of plot_metric more clear. Would you like to open a pull request for this? If not, I can help to do so.

[js850]

Thanks for the suggestion, @shiyu1994. I have created a PR to address this: #4709

[StrikerRUS]

Closed via #4709.

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