How to use Worksheet.EnableFormatConditionsCalculation in the xlwings API way

The EnableFormatConditionsCalculation member of the Worksheet object in Excel’s object model is a property that controls whether conditional formatting rules are recalculated automatically when worksheet data changes. When working with Excel via xlwings, this property is accessible and can be manipulated to optimize performance in workbooks with extensive or complex conditional formatting. By default, Excel recalculates conditional formats with each change to ensure visual accuracy, but this can slow down operations in large files. Disabling automatic recalculations allows for batch data updates without the overhead of repeated formatting evaluations, after which recalculations can be manually triggered or re-enabled.

In xlwings, this property is accessed through the api property of a worksheet object, which provides direct access to the underlying Excel VBA object model. The syntax for using it is straightforward: worksheet.api.EnableFormatConditionsCalculation. It is a Boolean property, meaning it accepts True or False values. Setting it to True (the default state) enables automatic calculation of conditional formats. Setting it to False disables these automatic calculations, which can be beneficial during macro execution or scripted data manipulation to speed up processing.

For example, consider a scenario where you are using a Python script with xlwings to update a large sales report worksheet that contains multiple conditional formatting rules highlighting top performers and outliers. If you update thousands of cells, having conditional formatting recalculate after each change would be inefficient. You can temporarily disable the calculations, perform all updates, and then re-enable it. Here is a code example:

import xlwings as xw

# Connect to the active workbook or open a specific one
wb = xw.Book.active
ws = wb.sheets['SalesData']

# Disable automatic conditional format calculation
ws.api.EnableFormatConditionsCalculation = False

# Perform bulk data updates
# For instance, update a range with new values
ws.range('A1:D1000').value = new_data_array # Assume new_data_array is a list of lists

# Re-enable automatic calculation
ws.api.EnableFormatConditionsCalculation = True

# Optionally, force a manual recalculation of conditional formats if needed
ws.api.Calculate

Another practical use is within a context manager to ensure the property is reset even if an error occurs during the update process. This approach enhances code robustness:

import xlwings as xw

wb = xw.Book('FinancialModel.xlsx')
ws = wb.sheets[0]

original_setting = ws.api.EnableFormatConditionsCalculation
try:
    ws.api.EnableFormatConditionsCalculation = False
    # Extensive data manipulation here
    ws.range('B2:F500').formula = '=RAND()*100' # Example formula insertion
finally:
    ws.api.EnableFormatConditionsCalculation = original_setting
    wb.save()