Creating and calling your own functions in Python

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Calling Python code from within Excel, and the vast functionality it unlocks Part five of a five-part series of blogs
Excel and Python are getting ever more intertwined: you can now use the PY function to write (and call) Python code from within an Excel worksheet Writing Python code within an Excel workbook to fill cells Returning dataframes from Python code to fill Excel ranges Manipulating images in Python within Excel How does Python reference modules within Excel? Creating and calling your own functions in Python (this blog)

Calling Python code from within Excel, and the vast functionality it unlocks

Part five of a five-part series of blogs

Excel and Python are getting ever more intertwined: you can now use the PY function to write (and call) Python code from within an Excel worksheet

Writing Python code within an Excel workbook to fill cells
Returning dataframes from Python code to fill Excel ranges
Manipulating images in Python within Excel
How does Python reference modules within Excel?
Creating and calling your own functions in Python (this blog)

Posted by Andy Brown on 27 October 2025

The secret to good programming is to encapsulate logic in functions - like this one to add two numbers together (obviously this logic already exists in Excel, but I'm using it to illustrate the principle):

def add_numbers_in_python(

first_number:int,

second_number:int

# add the two numbers

return first_number + second_number

A good way to incorporate these within Excel is to add them to the first worksheet in a workbook, and if necessary hide this:

We get the function to return an empty string. Normally you would not display the title in B1 or shading in B2!

You can then reference this elsewhere in your workbook:

Here we're using the function we defined on the first worksheet to add two numbers together.

Suddenly I can see vast vistas of possibility opening up!

Parts of this blog
Writing Python code within an Excel workbook to fill cells Returning dataframes from Python code to fill Excel ranges Manipulating images in Python within Excel How does Python reference modules within Excel? Creating and calling your own functions in Python (this blog)