csv - Modify an existing Excel file using Openpyxl in Python

Question

I am basically trying to copy some specific columns from a CSV file and paste those in an existing excel file[*.xlsx] using python. Say for example, you have a CSV file like this :

 col_1   col_2   col_3  col_4
  1        2       3     4
  5        6       7     8
  9       10      11    12 

So, i wanted to copy the both col_3 and col_4 and paste those in col_8 and col_9 in an existing excel file [which is a .XLSX format]. I have tried this in various way to solve, but could not find out the exact way. i tried something like this :

with open( read_x_csv, 'rb') as f:
    reader = csv.reader(f)
    for row in reader: 
            list1 = row[13] 
            queue1.append(list1)
            list2 = row[14] 
            queue2.append(list2)
            list3 = row[15] 
            queue3.append(list3)
            list4 = row[16] 
            queue4.append(list4)

and then

 rb = open_workbook("Exact file path.....")
 wb = copy(rb)
 ws = wb.get_sheet(0) 

 row_no = 0

 for item in queue1:
    if(item != ""):
            ii = int(item)
            ws.write(row_no,12,ii) 
            row_no = row_no + 1
            #ws.write(item)
            print item
    else:

            ws.write(row_no,12,item) 
            row_no = row_no + 1

  wb.save("Output.xls") 

but problem with this solution is it does not allow me to save as *.XLSX format which is strictly required for me.

I have tried to use Openpyxl as it can handle *.XLSX format, but could not find out a way to modify the existing excel file. can anyone please help on this?

Doubt : 1) Can we really read a whole column from a CSV file and store into an array/list using python? 2) Can we modify the existing excel file which is in .XLSX format using openpyxl or any other package?

Answer 1

You can try the following implementation

from openpyxl import load_workbook
import csv
def update_xlsx(src, dest):
    #Open an xlsx for reading
    wb = load_workbook(filename = dest)
    #Get the current Active Sheet
    ws = wb.get_active_sheet()
    #You can also select a particular sheet
    #based on sheet name
    #ws = wb.get_sheet_by_name("Sheet1")
    #Open the csv file
    with open(src) as fin:
        #read the csv
        reader = csv.reader(fin)
        #enumerate the rows, so that you can
        #get the row index for the xlsx
        for index,row in enumerate(reader):
            #Assuming space separated,
            #Split the row to cells (column)
            row = row[0].split()
            #Access the particular cell and assign
            #the value from the csv row
            ws.cell(row=index,column=7).value = row[2]
            ws.cell(row=index,column=8).value = row[3]
    #save the csb file
    wb.save(dest)

• Can we really read a whole column from a CSV file and store into an array/list using python? No, because files are read sequentially, csv reader cannot read a column of data to a row. Instead you may read the whole content and use izip and islice to get a particular column. You can also use numpy.array

• Can we modify the existing excel file which is in .XLSX format using openpyxl or any other package? Yes, see the example above