How to use Worksheet.Calculate in the xlwings API way

The Calculate method of the Worksheet object in Excel’s object model is a powerful tool for forcing a recalculation of all formulas within a specific worksheet. In xlwings, this functionality is exposed through the api property, which provides direct access to the underlying Excel object model. This is particularly useful when you have a workbook with manual calculation enabled or when you need to ensure that a specific sheet’s formulas are up-to-date before proceeding with further data analysis or visualization steps, without recalculating the entire workbook.

Functionality:
The primary function is to trigger a recalculation of all formulas on the worksheet. This is equivalent to pressing F9 while the specific sheet is active in the Excel application. It ensures that any dependent cells are updated based on the latest values of their precedent cells.

Syntax in xlwings:
The method is accessed via the api property of a Sheet object (which corresponds to a Worksheet). The general syntax is:

sheet.api.Calculate()

Where sheet is your xlwings Sheet object. This method does not take any parameters.

Important Consideration:
This method calculates only the formulas on the specified worksheet. If your formulas have dependencies on cells in other worksheets within the same workbook, those dependent formulas will also be recalculated to ensure consistency. However, it does not calculate formulas in other workbooks (external links).

Code Examples:

1. Basic Recalculation:
   This example opens a workbook, selects a specific sheet, and forces a calculation.

import xlwings as xw

# Open the workbook (or connect to an existing instance)
wb = xw.Book("financial_model.xlsx")
# Get the specific worksheet
data_sheet = wb.sheets["DataInput"]

# ... (some code that might change cell values programmatically) ...

# Force calculation of all formulas on the 'DataInput' sheet
data_sheet.api.Calculate()

2. Using in a Loop for Iterative Models:
   For models that require iterative solving or simulation, you can recalculate the sheet within a loop.

import xlwings as xw
import numpy as np

wb = xw.Book("simulation.xlsx")
model_sheet = wb.sheets["MonteCarlo"]

# Assume cell A1 holds a seed value for the simulation
for i in range(100):
    # Update an input cell with a new random value
    model_sheet.range("A1").value = np.random.rand()
    # Recalculate the sheet to update all dependent formulas (e.g., in outputs B1:B10)
    model_sheet.api.Calculate()
    # Read and store a result
    result = model_sheet.range("B10").value
    # ... process the result ...

3. Conditional Recalculation:
   Recalculate only if a certain condition is met, such as when manual calculation mode is active.

import xlwings as xw

app = xw.apps.active
wb = app.books.active
summary_sheet = wb.sheets["Summary"]

# Check if the application's calculation mode is set to manual
if app.api.Calculation == -4135: # -4135 corresponds to xlCalculationManual
    print("Manual calculation mode detected. Calculating 'Summary' sheet.")
    summary_sheet.api.Calculate()
else:
    print("Automatic calculation is on.")