How to use Application.Volatile in the xlwings API way

The Application.Volatile method in Excel, when invoked via xlwings, marks a user-defined function (UDF) as volatile. A volatile function recalculates every time a calculation occurs in any open workbook, not just when its direct precedents change. This is essential for functions that depend on dynamic data like real-time feeds, random numbers, or the current time. In xlwings, you typically use this within a Python function decorated with @xw.func to control its recalculation behavior.

Functionality:
It ensures that the UDF recalculates with every workbook calculation cycle. This is useful for functions that need to return updated values continuously, such as those fetching live data. However, overuse can slow down performance due to excessive recalculation.

Syntax in xlwings:
In xlwings, you call Application.Volatile within a UDF by accessing the Excel application object. The method takes one optional parameter:

• Volatile(True): Marks the function as volatile (default behavior if called without arguments).
• Volatile(False): Marks the function as non-volatile, meaning it recalculates only when its direct precedents change.

The xlwings API call format is:

xw.apps.active.api.Volatile(True) # For the active Excel application

Here, xw.apps.active refers to the active Excel application instance, and .api provides access to the underlying Excel object model. The parameter True sets volatility; use False to disable it.

Example Usage:
Consider a UDF that returns a random number, which should change on every recalculation. Without volatility, it might only update when explicitly triggered. The xlwings code below defines such a function:

import xlwings as xw
import random

@xw.func
def dynamic_random():
    # Access the Excel application and set the function as volatile
    xw.apps.active.api.Volatile(True)
    # Return a random number between 0 and 1
    return random.random()

# To use this, save the script and import it as an xlwings add-in or run it in an interactive session.