Pythonic Way To Set Entire Column To Value Pandas (settingwithcopywarning)

I want to set an entire column to a single string value. When doing so I get the (ever so popular) SettingWithCopy. I've tried to search SO before posting about this specific issue

Solution 1:

I was working on a similar requirement earlier today and I came across assign. I got rid of the copy warning without using pd.options.mode.chained_assignment = None. Here was my solution:

new_df_to_show_copy = dfp.loc[(dfp['A']>100) |(dfp['E']=='Unicorn')]
new_df_to_show_copy = new_df_to_show_copy.assign(Reason = 'what is with the copy warning')

# output:

       A    B           C   D        E                         Reason
9999.00.0  USA Pharma NaN  Unicorn  what iswith the copy warning    

assign will leave a copy of the dataframe, and there is no inplace=True parameter. so just reassigning the value worked for me.