Python: How to turn a dictionary of Dataframes into one big dataframe with column names being the key of the previous dict?

Question

So my dataframe is made from lots of individual excel files, each with the the date as their file name and the prices of the fruits on that day in the spreadsheet, so the spread

Answer 1

Something like this could work: loop over the dictionary, add the constant column with the dictionary key, concatenate and then set the date as index

pd.concat(
    (i_value_df.assign(date=i_key) for i_key, i_value_df in d.items())
).set_index('date')