Python win32com 'Invalid number of parameters'

I am trying to use win32com to convert multiple xlsx files into xls using the following code:

import win32com.client

f = r"./input.xlsx"
xl = win32com.client.gencache.EnsureDispatch('Excel.Application')
wb = xl.Workbooks.Open(f)
xl.ActiveWorkbook.SaveAs("./somefile.xls", FileFormat=56)

which is failing with the following error:

Traceback (most recent call last):
  File "xlsx_conv.py", line 6, in <module>
    xl.ActiveWorkbook.SaveAs("./somefile.xls", FileFormat=56)
  File "C:\python27\lib\site-packages\win32com\gen_py\00020813-0000-0000-C000-000000000046x0x1x9.py", line 46413, in SaveAs
    , Local, WorkIdentity)
pywintypes.com_error: (-2147352562, 'Invalid number of parameters.', None, None)

Some more details:

I can do other commands to the workbook i.e. wb.Worksheets.Add()and set xl.Visible=True to view the workbook. and even do wb.Save() but can't do a wb.SaveAs()

Solution

The COM exception is due to the missing filename argument as f = r"./input.xlsx" cannot be found. Had you used Excel 2013+, you would have received a more precise exception message with slightly different error code:

(-2147352567, 'Exception occurred.', (0, 'Microsoft Excel', "Sorry, we couldn't find ./input.xlsx. Is it possible it was moved, renamed or deleted?", 'xlmain11.chm', 0, -2146827284), None)

While your path does work in Python's native context pointing to the directory the called .py script resides, it does not in interfacing with an external API, like Windows COM, as full path is required.

To resolve, consider using Python's built-in os to extract the current directory path of script and concatenate with os.path.join() in the Excel COM method. Also, below uses try/except/finally to properly end the Excel.exe process in background regardless if exception is raised or not.

import os
import win32com.client as win32

cd = os.path.dirname(os.path.abspath(__file__))

try:
    f = os.path.join(cd, "input.xlsx")
    xl = win32.gencache.EnsureDispatch('Excel.Application')
    wb = xl.Workbooks.Open(f)
    xl.ActiveWorkbook.SaveAs(os.path.join(cd, "input.xls"), FileFormat=56)
    wb.Close(True)

except Exception as e:
    print(e)

finally:
    wb = None
    xl = None