How to use Application.DDERequest in the xlwings API way

The DDERequest method of the Application object in Excel is a legacy function used to retrieve data from an external application via Dynamic Data Exchange (DDE). This method allows Excel to act as a DDE client, requesting specific information from a DDE server application. While DDE is an older technology largely superseded by more modern methods like COM or various APIs, understanding DDERequest can be crucial for maintaining or interfacing with legacy systems that still rely on DDE communication channels. In the context of xlwings, which provides a Pythonic way to automate Excel, you can access this method through the Application object.

Functionality
The primary function of DDERequest is to establish a DDE conversation with a server application and request a specific data item. It is used to fetch real-time or static data from programs that support DDE, such as some financial data feeds, scientific instruments, or older database systems. The method initiates a request for a particular item within an established DDE channel.

Syntax
In xlwings, the DDERequest method is accessed via the Application object. The general syntax is as follows:

app.application.DDERequest(Channel, Item)

• Channel (Required): A Long integer that represents the channel number returned by a previous DDEInitiate call. This channel identifies an open DDE conversation with a server application.
• Item (Required): A String that specifies the data item being requested from the DDE server. The format and meaning of this string are defined by the server application. It often resembles a cell reference (e.g., “R1C1”) or a named range specific to the server.

Parameters and Usage
The method requires a pre-established DDE channel. Typically, you use the DDEInitiate method first to open a channel to a specific server and topic. The Item parameter is entirely dependent on the DDE server’s protocol. Common examples include requesting specific stock prices, instrument readings, or database fields. The method returns a Variant containing the requested data, which could be a number, string, or array.

Code Example
The following xlwings code example demonstrates how to use DDERequest to request data from a hypothetical DDE server. The example assumes a server application named “MyServer” with a topic “Prices”, and requests the item “StockXYZ”.

import xlwings as xw

# Connect to the active Excel instance or start a new one
app = xw.apps.active

# First, initiate a DDE channel (this is typically done via Excel's DDEInitiate method).
# Note: xlwings does not have a direct wrapper for DDEInitiate, so we use the underlying API.
# This requires the channel number from a successful DDEInitiate call.
# For demonstration, we assume channel number 5 is already open.
channel_number = 5 # This would come from a prior DDEInitiate call.

# Use DDERequest to get data for the item "StockXYZ"
try:
    requested_data = app.api.DDERequest(Channel=channel_number, Item="StockXYZ")
    print(f"Data received via DDE: {requested_data}")
except Exception as e:
    print(f"DDERequest failed: {e}")

# In a real-world scenario, you would also close the channel using DDETerminate.
# app.api.DDETerminate(Channel=channel_number)