Python win32com excel process file access or permissions issue - excel

Question

I'm trying to resolve a permissions/file access issue with a python win32com excel process run from a flask app.
I have a python script that runs a VBA macro that works locally on the flask app server when I invoke it manually, but throws an error when I hook it up to an endpoint and query it externally through HTTP.
The script is a simple test case. It opens excel and runs a VBA macro that writes a text file with a timestamp in the same directory as the macro workbook.
def testXL():
try:
import pythoncom
pythoncom.CoInitialize()
fn = 'vbRender.xlsm'
fp = os.path.join(cc.appRootDir,"workingProductDir",fn)
xl=win32com.client.Dispatch("Excel.Application")
xl.Workbooks.Open(os.path.abspath(fp), ReadOnly=1)
xl.Application.Run("%s!DebugEnvironment.writeFileTest"%(fn))
del xl
return "Success"
except:
excInfo = sys.exc_info()
excDetails = ''.join(traceback.format_exception(*excInfo))
return "%s: %s"%(excInfo,excDetails)
This runs successfully on my flask app server when I invoke it from command line or IDLE.
When I hook it up to a flask endpoint like this:
#app.route('/dev/testxl')
def testXL():
...
and then hit the endpoint from another machine I get the following error:
(com_error(-2147352567, 'Exception occurred.', (0, 'Microsoft Excel', "Microsoft Excel cannot access the file 'C:\\...\\workingProductDir\\vbRender.xlsm'. There are several possible reasons:\n\n• The file name or path does not exist.\n• The file is being used by another program.\n• The workbook you are trying to save has the same name as a currently open workbook.", 'xlmain11.chm', 0, -2146827284), None), ): Traceback (most recent call last): File "C:\...\flaskAppSocket.py", line 1372, in testXL xl.Workbooks.Open(os.path.abspath(fp), ReadOnly=1) File ">", line 5, in Open pywintypes.com_error: (-2147352567, 'Exception occurred.', (0, 'Microsoft Excel', "Microsoft Excel cannot access the file 'C:\\...\\workingProductDir\\vbRender.xlsm'. There are several possible reasons:\n\n• The file name or path does not exist.\n• The file is being used by another program.\n• The workbook you are trying to save has the same name as a currently open workbook.", 'xlmain11.chm', 0, -2146827284), None)
It doesn't appear to be a concurrent use issue, since I can boot up an instance of IDLE on the flask server machine and run the script locally between attempts to access the endpoint via HTTP. It is always successful when run manually on the server.
It looked to me like a permissions issue, but my flask app is very clearly running with highest level privileges. To confirm, I created an endpoint that just writes a file to the same folder using python, instead of an excel VBA process. The following endpoint works:
#app.route('/dev/testfilewrite')
def testWriteFile():
n = datetime.datetime.now()
fp = os.path.join(cc.appRootDir,"workingProductDir",
"%s log test.txt"%(n.strftime("%Y-%m-%d-%H-%M-%S")))
f = open(fp, "w")
f.write("this is a test")
return "Success"
So it has something to do with that particular file or use.
After restarting my flask app machine and trying again with no resolution, I am at a loss as to how to proceed. The exception printout clearly shows that it is failing before it gets to the macro, in the process of opening the file. How can I troubleshoot this further?