In [2]: import pandas as pd

In [3]: import dask.dataframe as dd

In [4]: from datetime import date, datetime, timedelta

In [5]: dfpd = pd.DataFrame({'a': [date(2020,1,1)]}, dtype='date32[pyarrow]')

In [6]: df = dd.from_pandas(dfpd)

In [7]: df
Out[7]: 
Dask DataFrame Structure:
                                  a
npartitions=1                      
0              date32[day][pyarrow]
0                               ...
Dask Name: frompandas, 1 expression
Expr=df

In [8]: df.assign(b=df['a'][0])
Out[8]: 
Dask DataFrame Structure:
                                  a       b
npartitions=1                              
0              date32[day][pyarrow]  object
0                               ...     ...
Dask Name: assign, 4 expressions
Expr=Assign(frame=df)