Append existing excel sheet with new dataframe using python pandas

Question

I currently have this code. It works perfectly.

It loops through excel files in a folder, removes the first 2 rows, then saves them as individual excel files, and it also saves the files in the loop as an appended file.

Currently the appended file overwrites the existing file each time I run the code.

I need to append the new data to the bottom of the already existing excel sheet ('master_data.xlsx)

dfList = []
path = 'C:\\Test\\TestRawFile' 
newpath = 'C:\\Path\\To\\New\\Folder'

for fn in os.listdir(path): 
  # Absolute file path
  file = os.path.join(path, fn)
  if os.path.isfile(file): 
    # Import the excel file and call it xlsx_file 
    xlsx_file = pd.ExcelFile(file) 
    # View the excel files sheet names 
    xlsx_file.sheet_names 
    # Load the xlsx files Data sheet as a dataframe 
    df = xlsx_file.parse('Sheet1',header= None) 
    df_NoHeader = df[2:] 
    data = df_NoHeader 
    # Save individual dataframe
    data.to_excel(os.path.join(newpath, fn))

    dfList.append(data) 

appended_data = pd.concat(dfList)
appended_data.to_excel(os.path.join(newpath, 'master_data.xlsx'))

I thought this would be a simple task, but I guess not. I think I need to bring in the master_data.xlsx file as a dataframe, then match the index up with the new appended data, and save it back out. Or maybe there is an easier way. Any Help is appreciated.

Answer 1

A helper function for appending DataFrame to existing Excel file:

import os
from openpyxl import load_workbook


def append_df_to_excel(filename, df, sheet_name='Sheet1', startrow=None,
                       truncate_sheet=False, 
                       **to_excel_kwargs):
    """
    Append a DataFrame [df] to existing Excel file [filename]
    into [sheet_name] Sheet.
    If [filename] doesn't exist, then this function will create it.

    @param filename: File path or existing ExcelWriter
                     (Example: '/path/to/file.xlsx')
    @param df: DataFrame to save to workbook
    @param sheet_name: Name of sheet which will contain DataFrame.
                       (default: 'Sheet1')
    @param startrow: upper left cell row to dump data frame.
                     Per default (startrow=None) calculate the last row
                     in the existing DF and write to the next row...
    @param truncate_sheet: truncate (remove and recreate) [sheet_name]
                           before writing DataFrame to Excel file
    @param to_excel_kwargs: arguments which will be passed to `DataFrame.to_excel()`
                            [can be a dictionary]
    @return: None

    Usage examples:

    >>> append_df_to_excel('d:/temp/test.xlsx', df)

    >>> append_df_to_excel('d:/temp/test.xlsx', df, header=None, index=False)

    >>> append_df_to_excel('d:/temp/test.xlsx', df, sheet_name='Sheet2',
                           index=False)

    >>> append_df_to_excel('d:/temp/test.xlsx', df, sheet_name='Sheet2', 
                           index=False, startrow=25)

    (c) [MaxU](https://stackoverflow.com/users/5741205/maxu?tab=profile)
    """
    # Excel file doesn't exist - saving and exiting
    if not os.path.isfile(filename):
        df.to_excel(
            filename,
            sheet_name=sheet_name, 
            startrow=startrow if startrow is not None else 0, 
            **to_excel_kwargs)
        return
    
    # ignore [engine] parameter if it was passed
    if 'engine' in to_excel_kwargs:
        to_excel_kwargs.pop('engine')

    writer = pd.ExcelWriter(filename, engine='openpyxl', mode='a')

    # try to open an existing workbook
    writer.book = load_workbook(filename)
    
    # get the last row in the existing Excel sheet
    # if it was not specified explicitly
    if startrow is None and sheet_name in writer.book.sheetnames:
        startrow = writer.book[sheet_name].max_row

    # truncate sheet
    if truncate_sheet and sheet_name in writer.book.sheetnames:
        # index of [sheet_name] sheet
        idx = writer.book.sheetnames.index(sheet_name)
        # remove [sheet_name]
        writer.book.remove(writer.book.worksheets[idx])
        # create an empty sheet [sheet_name] using old index
        writer.book.create_sheet(sheet_name, idx)
    
    # copy existing sheets
    writer.sheets = {ws.title:ws for ws in writer.book.worksheets}

    if startrow is None:
        startrow = 0

    # write out the new sheet
    df.to_excel(writer, sheet_name, startrow=startrow, **to_excel_kwargs)

    # save the workbook
    writer.save()

Tested with the following versions:

• Pandas 1.2.3
• Openpyxl 3.0.5

---

Usage examples:

filename = r'C:\OCC.xlsx'

append_df_to_excel(filename, df)

append_df_to_excel(filename, df, header=None, index=False)

append_df_to_excel(filename, df, sheet_name='Sheet2', index=False)

append_df_to_excel(filename, df, sheet_name='Sheet2', index=False, startrow=25)

---

Old answer: it allows you to write a several DataFrames to a new Excel file.

You can use openpyxl engine in conjunction with startrow parameter:

In [48]: writer = pd.ExcelWriter('c:/temp/test.xlsx', engine='openpyxl')

In [49]: df.to_excel(writer, index=False)

In [50]: df.to_excel(writer, startrow=len(df)+2, index=False)

In [51]: writer.save()

c:/temp/test.xlsx:

PS you may also want to specify header=None if you don't want to duplicate column names...

UPDATE: you may also want to check this solution