how to properly apply a vector based function to a pandas dataframe column?

I am trying to apply a function that returns an specific date in an specific format, however I am struggling to apply this function to a new pandas dataframe column.

Here’s what I got so far:

import pandas as pd
import datetime

actual_date = datetime.now()
actual_date = datetime.strptime("{}/{}/{}".format('01', actual_date.month, actual_date.year), "%d/%m/%Y")

def set_date(actual_date):
    result = actual_date - dateutil.relativedelta.relativedelta(months=1)
    print(datetime.strftime(result, "%d/%m/%Y"))

df['date'] = df.apply(lambda x: set_date(x[actual_date]), axis=1)

The next error arises:

KeyError: datetime.datetime(2021, 2, 1, 0, 0)

Expected output could be a pandas dataframe column where row-values are set_date output.

How could I accomplish this task?

Answer

The issue was related to the setting of x for lambda:

df['date']= df.apply(lambda x: set_date(actual_date), axis=1)