How to use Application.Calculation in the xlwings API way

The Application.Calculation property in Excel is a crucial setting that determines how formulas are recalculated within a workbook. In xlwings, this property allows you to control the calculation mode programmatically, which is essential for optimizing performance, especially when dealing with large or complex spreadsheets that involve numerous formulas and dependencies.

Functionality
This property controls the Excel calculation engine’s mode. You can set it to force automatic recalculation, manual recalculation, or a semi-automatic mode. This is particularly useful when you are writing data to many cells via xlwings and want to prevent Excel from recalculating after each write operation, which can significantly slow down execution. By setting calculation to manual, performing all data updates, and then setting it back to automatic (or triggering a manual calculation), you can drastically improve the performance of your scripts.

Syntax and Parameters
In xlwings, you access this property through the app object, which represents the Excel Application. The syntax is straightforward:
app.calculation
This property is both gettable and settable. When setting it, you assign one of the following constants, which are available directly in xlwings:

Constant (from xlwings.constants)	Value	Description
xlwings.constants.Calculation.xlCalculationAutomatic	-4105	Excel controls recalculation.
xlwings.constants.Calculation.xlCalculationManual	-4135	Recalculation only occurs when explicitly requested (e.g., by pressing F9).
xlwings.constants.Calculation.xlCalculationSemiautomatic	2	Recalculation is automatic except for data tables.

You can also use the raw numeric values, but using the named constants is recommended for better code readability.

Code Examples
Here are practical examples of using the app.calculation property with xlwings:

1. Checking the Current Calculation Mode:

import xlwings as xw
app = xw.apps.active # Get the active Excel application
current_mode = app.calculation
print(f"Current calculation mode is: {current_mode}")

2. Setting Calculation to Manual for Performance:
   This is a common pattern for batch operations.

import xlwings as xw
from xlwings.constants import Calculation

app = xw.apps.active
original_mode = app.calculation # Save the original state

# Set to manual to prevent recalculations during data writes
app.calculation = Calculation.xlCalculationManual

# Perform your data operations (e.g., writing to many cells)
wb = app.books.active
sht = wb.sheets[0]
for row in range(2, 1002):
    sht.range(f'A{row}').value = row * 10
    # Without manual calculation, Excel would recalculate here 1000 times!

# After data is written, trigger a single full calculation
wb.app.calculate() # Equivalent to pressing F9 in Excel

# Restore the original calculation mode
app.calculation = original_mode

3. Setting Calculation to Automatic:

import xlwings as xw
from xlwings.constants import Calculation

app = xw.apps.active
app.calculation = Calculation.xlCalculationAutomatic
print("Calculation set to Automatic.")