Why is pandas not formatting dates with date_format?

Why is pandas not formatting dates with date_format argument of to_csv?

pandas.DataFrame([datetime.datetime.now().date()]).to_csv(date_format="%Y %b")
',0\n0,2025-07-31\n'

If you use .dtypes to check what you have in dataframe then you should see that date is kept as object, but datetime is kept as datetime64[ns] and this can make difference.

import pandas as pd
import datetime

df = pd.DataFrame({
    "date": [datetime.datetime.now().date()], 
    "datetime": [datetime.datetime.now()], 
})

print(df.dtypes)

date                object
datetime    datetime64[ns]

But if you check single value then you see that this object keeps it as datetime.date() and you can still use .apply(lambda x:x.strftime("%Y %b") before sending to csv.

(but it doesn't allow to use .dt.strftime like for datetime64[ns])

df["date"] = df["date"].apply(lambda x:x.strftime("%Y %b"))

df["datetime"] = df["datetime"].dt.strftime("%Y %b")

to_csv() doesn't allow to set format for selected columns (with objects) so it has to be done before sending to file.