How to use Application.CalculateBeforeSave in the xlwings API way

The Application.CalculateBeforeSave property in Excel’s object model controls whether calculation occurs automatically before a workbook is saved. This setting is particularly useful in large or complex workbooks where manual calculation mode is enabled to improve performance during data entry or manipulation. By setting CalculateBeforeSave to True, you ensure all formulas are recalculated with the latest data upon saving, preventing outdated results. When set to False, Excel skips this recalculation step, which can speed up the saving process but may leave formulas unupdated.

In xlwings, you can access this property through the Application object. The syntax is straightforward: app.calculate_before_save, where app represents the xlwings App instance. This property accepts a Boolean value: True enables pre-save calculation, and False disables it. It’s important to note that this is a global setting applied to the Excel application instance, affecting all open workbooks managed by that instance. You can both retrieve the current setting and modify it as needed.

For example, to check the current CalculateBeforeSave setting using xlwings, you can use the following code:

import xlwings as xw

# Connect to the active Excel instance
app = xw.apps.active

# Get the current CalculateBeforeSave value
current_setting = app.calculate_before_save
print(f"CalculateBeforeSave is currently set to: {current_setting}")

To change the setting, assign a new Boolean value. The code below disables calculation before saving, which might be beneficial for performance in large workbooks:

import xlwings as xw

app = xlwings.apps.active
# Disable calculation before saving
app.calculate_before_save = False
print("CalculateBeforeSave has been disabled.")

If you need to enable it again to ensure data accuracy, simply set it to True:

app.calculate_before_save = True
print("CalculateBeforeSave has been enabled.")

A practical use case involves toggling this property during automated processes. For instance, if you’re running a script that makes numerous changes and saves intermittently, disabling CalculateBeforeSave can reduce overhead. After completing all updates, you can re-enable it and force a manual recalculation before the final save:

import xlwings as xw

app = xw.apps.active
workbook = app.books.active

# Disable calculation to speed up intermediate saves
app.calculate_before_save = False
# Perform data manipulations...
workbook.save('temp_save.xlsx')

# Re-enable calculation and recalculate before final save
app.calculate_before_save = True
workbook.calculate()
workbook.save('final_save.xlsx')