How to use Application.DDEAppReturnCode in the xlwings API way

The DDEAppReturnCode property of the Application object in Excel is a read-only property that returns the status code from the last Dynamic Data Exchange (DDE) operation. DDE is an older inter-process communication protocol that allows applications to exchange data. While modern automation typically uses other methods like COM (which xlwings utilizes), this property can be useful for debugging or maintaining legacy Excel applications that interact with DDE servers. The returned integer code indicates success or the specific type of error that occurred during the DDE conversation.

In xlwings, you access this property through the api property of the main App or Book objects, which exposes the raw Excel VBA object model. The syntax is straightforward as it takes no arguments.

Syntax:

xlwings.App.api.DDEAppReturnCode

or, if you have a specific workbook instance:

wb.api.Application.DDEAppReturnCode

Where:

• The property is accessed directly and returns an Integer value.

The meaning of the return codes is defined by the DDE protocol and the applications involved. Common codes include:

Code	Typical Meaning
0	Success / No Error
1	The topic was not understood by the server.
2	The server did not respond.
7	Unknown error.

Important Note: The exact meaning of non-zero codes can vary depending on the DDE server application. You should consult the documentation for the specific application you are communicating with.

Example:
The following xlwings code initiates a DDE operation (a very legacy example) and then checks the return code to see if it was successful.

import xlwings as xw

# Start Excel application
app = xw.App(visible=False)
wb = app.books.add()

# Attempt a legacy DDE operation (e.g., initiating a conversation with "MyServer" on topic "System")
# Note: This is a pseudo-example, as modern xlwings doesn't have direct DDE methods.
# You would typically use the Excel VBA object model via .api for such calls.
try:
    # Simulating a DDE operation using the Excel object model
    # In VBA, this might be: channel = Application.DDEInitiate(app:="MyServer", topic:="System")
    # In xlwings, you would use:
    channel = app.api.DDEInitiate("MyServer", "System")
    print(f"DDE channel opened: {channel}")
except Exception as e:
    print(f"An error occurred during DDEInitiate: {e}")
finally:
    # Check the status code of the last DDE operation
    return_code = app.api.DDEAppReturnCode
    print(f"DDEAppReturnCode: {return_code}")

# Interpret the code
if return_code == 0:
    print("Last DDE operation was successful.")
else:
    print(f"Last DDE operation failed with error code: {return_code}")

# Clean up: Close the channel if it was opened, then quit Excel
if 'channel' in locals():
    app.api.DDETerminate(channel)
wb.close()
app.quit()