[Python] Construct date column from year, month and day in Polars dataframe

Consider the following Polars dataframe:


df = pl.DataFrame({
'date': ['2022-01-01', '2022-02-01', '2022-03-01']
})

df.with_column(pl.col('date').str.strptime(pl.Date, fmt='%Y-%m').cast(pl.Datetime)).alias('year-month')



Currently the dataframe is:

date
2022-01-01
2022-02-01
2022-03-01

The desired output is:

date year-month
2022-01-01 2022-01
2022-02-01 2022-02
2022-03-01 2022-03

I have tried:


df.with_column(pl.col('date').str.strptime(pl.Date, fmt='%Y-%m').cast(pl.Datetime)).alias('year-month')



I get:

SchemaError: invalid series dtype: expected Utf8, got datetime[ns]

Thanks so much!!!

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