Python for Excel

Overview

Install the add-in . Create an Excel function from a Python function in two easy steps as follows:

1. Write a Python function

Using the add-in code editor, write or paste your function code, e.g.:

def hello(name):
    """ Returns a greeting. """
    return f"Hello {name}!"

2. Run as an Excel function

Python code is stored in workbook settings, and the function is added to the name manager as follows:

=LAMBDA(name, BOARDFLARE.EXEC("hello", name))

The function is now available for use in the workbook as follows:

=HELLO(name)

How it works

When you save this code, the Python function name hello and argument name are parsed to create a LAMBDA function =LAMBDA(name, BOARDFLARE.EXEC("hello", name)) which is saved to the name manager with the name HELLO. The Python code for the function named hello is saved to the workbook settings  so it is embedded in the workbook. The first line of the Python function docstring is also added as a comment to the name manager to provide an autocomplete description.

Each time the function is invoked, BOARDFLARE.EXEC loads the code from the workbook settings and runs it with the argument. Since the code and LAMBDA are both stored in the workbook, anyone who uses the workbook can use the function. If they don’t have the add-in installed, Excel will automatically prompt them to do so.

Features

Some key features of the add-in are as follows:

✅ Use Python in formulas and LAMBDA functions.
🆓 Free for unlimited use.
🌐 Works in Excel for web as well as desktop.
☁️ Runtime has network access for API calls (needs CORS).
📦 Import custom packages (pure Python only).
🔒 Code is stored in your workbook and runs locally.

Limitations

• Your Python code must be a function. All data is passed to the function as arguments.
• Excel PY range references, e.g. xl("Sheet1!A1:A10"), cannot be used to pass data to the code.
• Local files cannot be accessed due to browser security restrictions.
• *args and **kwargs are not supported because LAMBDA functions do not support repeating arguments.

Importing Packages

Pyodide  is the Python runtime used by the add-in, and includes a number of built-in packages . Any imports of built-in packages (e.g. import pandas as pd) will work without any additional installation required. However, you can only use the version of the package that is included in the Pyodide runtime, which may not be the latest version.

You may also import any pure Python (OS-independent ) packages hosted on PyPI  using micropip as follows:

import micropip
await micropip.install(['azure-ai-textanalytics', 'textdistance'])
# Continue with your code...

Note: Prior to version 1.4.0, packages were automatically installed from PyPI, but this only worked if the package name was the same as the import name, which is not always the case. To avoid this confusion, you must now explicitly install packages using micropip as shown above.

Type Conversion

The following type conversions will take place on the arguments passed to your function from Excel:

*Excel stores dates as numbers in serial format, and since we have no way to distinguish these from non-date numbers, they are not converted to datetime objects, and simply become a Python float. If you want to convert an Excel serial to a Python datetime, you can use the following code:

from datetime import datetime, timedelta
 
def excel_date_to_datetime(serial):
    return datetime(1899, 12, 30) + timedelta(days=serial)

The value returned by your Python function will similarly be converted to the corresponding Excel type as follows:

*Assumes formula is in cell A1.

If your function returns another Python type such as a list, set, or other non-scalar types, an error will be thrown. We have support for converting numpy and pandas types to help reduce errors, but recommend you not rely on these.

Example Functions

We have a growing collection of example functions that you can use as a starting point for your own code. You can find these in the Functions section of the website.

FAQ

Changelog

1.4.0 - 2025-06-20

• Pyodide  updated to v0.27.5, which updates Python to 3.13.2 and many built-in packages  such as pandas.
• Imports for any package not in built-in packages  must now be explicitly imported using micropip.
• Insert result, not formula option in function dialog for cases where you want a static result.
• Charts: if a function returns an image data URL, insert result will insert image.
• Python function names can now be mixed case.
• OneDrive: Permissions are now scoped to AppFolder  only; added support Microsoft personal accounts.