运行dask程序报错：Task exception was never retrieved

提示Task exception was never retrieved。

代码如下：

import dask.dataframe as dd
from dask.distributed import Client, LocalCluster

import pandas as pd
cluster = LocalCluster(dashboard_address=None)
client = Client(cluster)
df = pd.DataFrame([[1, 1, 1], [2, 2, 2]])
df = dd.from_pandas(df, npartitions=1)
print(df.head())

这个问题在dask社区中有讨论（ https://github.com/modin-project/modin/issues/843 ），具体原因还不是特别清楚，讨论过程看可能与modin或者ray有关系，解决方法很简单，加入main方法即可：

import dask.dataframe as dd
from dask.distributed import Client, LocalCluster

import pandas as pd

if __name__ == '__main__':
    cluster = LocalCluster(dashboard_address=None)
    client = Client(cluster)
    df = pd.DataFrame([[1, 1, 1], [2, 2, 2]])
    df = dd.from_pandas(df, npartitions=1)
    print(df.head())