Update Links in for Excel Spreadsheet Using Python

Question

I am running simulations in Python that generate output that need to be directly consumed by a modeler in their excel workbooks. I have generated code that will directly output my data into their excel spreadsheet template. The code I have generated to output the data directly to their template is fine, but the problem I am running into is that the modeler has a series of workbooks that are "linked" together. If I insert my data into their spreadsheet, the links to that workbook do no update unless the user physically opens the workbook to "Edit Links" -> "Update Values". If there was one workbook, then the user can simply open the workbook with no problem. In reality, there will be over 100 workbooks that need the links updated. Unfortunately, there is nothing I can do to change the modeler's approach in linking workbooks -- the only thing I can do is accommodate their approach.

My goal is to create a Python solution that will allow me to 1) Generate the simulated Data, 2) Insert my generated data into the modeler's workbook, and 3) Update all of the links between workbooks. Ultimately, in order to be streamlined, I want to be able to do all three in one end-to-end python program. I have solved (1) and (2), and I have a solution for (3) that almost works. I have generated the following functional script:

from win32com.client import Dispatch
import pandas as pd
from openpyxl import load_workbook
import os
import time

def run_macro(workbook_name, vba_sub, com_instance):
    wb = com_instance.workbooks.open(workbook_name)
    wb.RefreshAll()
    xl_module = wb.VBProject.VBComponents.Add(1)
    xl_module.CodeModule.AddFromString(vba_sub.strip())
    com_instance.Application.Run('UpdateLinkValues')
    wb.Save()
    wb.Close()

    return True

def main():
    dir_root  = ("C:\\Model_Spreadsheets")

    vba_sub = \
        '''
        sub UpdateLinkValues()
            Application.AskToUpdateLinks = False
            ActiveWorkbook.UpdateLink Name:=ActiveWorkbook.LinkSources
        end sub
        '''

    xl_app = Dispatch("Excel.Application")
    xl_app.Visible = False
    xl_app.DisplayAlerts = False

    for root, dirs, files in os.walk(dir_root):
        for fn in files:
            if fn.endswith(".xlsx") and fn[0] is not "~":
                run_macro(os.path.join(root, fn), vba_sub, xl_app)
    xl_app.Quit()


if __name__ == "__main__":
    main()

This script is really close to the correct solution I am looking for, but I run into a VBA error seemingly 'randomly':

run-time error '1004' method 'updatelink' method of object '_workbook' failed

This error does appear each time I try to run this script, but it does not occur for the same workbook each time -- sometimes, it occurs on the first workbook, sometimes on the 15th, etc...

I have an option to debug in VBA, and the only way that I can continue on to the next workbook is if I change the macro to

sub UpdateLinkValues()
    Application.AskToUpdateLinks = False
end sub

if I run this macro and exit debug, the program will continue to run until it encounters the same error again. My first thought was that maybe there is a timing issue between me opening the workbook and trying to run the macro. A workaround that I have found is that I can change the macro and the app visibility:

vba_sub = \
    '''
    sub UpdateLinkValues()
        Application.AskToUpdateLinks = False
    end sub
    '''

and

xl_app.Visible = True

This works fine, but I am not a fan of having each of the workbooks open and close because it takes a long time. My question is, does anyone know why this run-time error is coming up -- with a solution? Or perhaps, does anyone know how to intercept this run-time error in Python as an exception? If I can intercept this error as an exception in python, then I could use my alternative solution for those particulars workbooks.

Thanks in advance!

Answer 1

Consider having Python directly run the method UpdateLink with the COM objects you initialize, namely the xl_app and wb objects. No need to build a macro in each workbook and then call it.

Below UpdateLink() is wrapped in a try/except/finally block in case workbook has no links as LinkSources will return an Empty value, raising a COM exception, the very error you receive:

run-time error '1004' method 'updatelink' method of object '_workbook' failed

Also be sure to uninitialize objects (a good best practice in VBA too: Set wb = Nothing ) after use to free CPU resources else they remain as background processes until garbage collection.

def run_macro(workbook_name, com_instance):
    wb = com_instance.workbooks.open(workbook_name)
    com_instance.AskToUpdateLinks = False
    try:
       wb.UpdateLink(Name=wb.LinkSources())

    except Exception as e:
       print(e)

   finally:
       wb.Close(True)
       wb = None    
    return True

def main():
    dir_root  = ("C:\\Model_Spreadsheets")

    xl_app = Dispatch("Excel.Application")
    xl_app.Visible = False
    xl_app.DisplayAlerts = False

    for root, dirs, files in os.walk(dir_root):
        for fn in files:
            if fn.endswith(".xlsx") and fn[0] is not "~":
                run_macro(os.path.join(root, fn), xl_app)
    xl_app.Quit()
    xl = None

Aside - though VBA ships by default with Excel and MS Office applications, it is actually a separate component. To check, under Tools \\ References in VBA IDE, you will see VBA is the first checked item, nothing built-in. In fact, VBA does exactly what you are doing in Python: making a COM interface to the Excel Object Library. So in a sense VBA is just as related to Excel and Python is!