My Approach in Integrating Excel and Python

Introduction

In this post I will share how I integrate Python scripts with Excel.

The Problem

I found that Excel formulas already satisfy >90% of my needs. However, on certain cases it’s not enough, and this is where Python is needed. Cases such as:

• Scraping data from the internet
• Pre-processing some messy data (such as poorly formatted CSV file generated from a third-party program)
• Running complex calculations on a huge amount of data

I want to be able to run a macro from Excel (e.g. by clicking a button) and have the processed data somehow be pasted to the Excel sheet. However, by default Excel and Python are not connected with each other.

The Solution

After working several projects that have this problem, I found out that the ideal solution need to separate as much as possible between the Python script and the Excel file. The reasons I want to separate/decouple between Excel and Python are so:

• I can debug/run the Python script without opening the Excel
• I become more confident when editing the Excel file, and not afraid I would break the macro (to some extent)

There is an excellent Python library called xlwings, but I do not use it since the script would read or modify the Excel file directly.

The following is my solution to this problem:

1. Have the Python script copy the desired data to clipboard, and have the VBA paste from clipboard to a certain location in the Excel file
2. If some input data is required for the Python script, then it need to be in the form of “command line arguments”

Example Cases

Let’s work through a very simple example. In a folder, the files are as follows:

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+- Folder/
   +-- Document.xlsm
   +-- load_data.py

The content of load_data.py is:

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import pandas as pd
df = pd.DataFrame({'Name':['Joe', 'Mike'], 'Age':[32, 34]})
df.to_clipboard(index=False)

Meanwhile, the Excel file has a macro like this:

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Sub LoadData()
    Dim cmd As String
    Dim sht As Worksheet
    ChDrive ThisWorkbook.Path
    ChDir ThisWorkbook.Path

    sht = Sheets("Sheet1")
    cmd = "python load_data.py"

    Dim shell As Object
    Dim errorCode As Integer
    Set shell = CreateObject("WScript.Shell")
    errorCode = shell.Run(cmd, vbNormalFocus, waitOnReturn:=True)
    If errorCode = 0 Then
        sht.range("A1").pastespecial
    Else
        MsgBox "Failed to load data!"
    End If
End Sub

(Even better if, instead of referencing cell A1 like that, you use named references; see Use the Name Manager in Excel for more information.)

Now, if the above macro is executed, then the following data will be pasted into Excel:

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| Name  | Age |
--------------|
| Joe   | 32  |
| Mike  | 34  |

Disadvantage to This Approach

The disadvantage of this approach is that you cannot paste multiple data; so, you must create a new script. This could be a problem from performance perspective: invoking a Python script takes a significant amount of time, more so if you load a large package like Pandas. On some cases, you may want to just use the xlwings library.

Conclusion

In this post I have shared how I integrate Excel and Python. I hope the method I have described could be useful for you. Have a nice day!