[Python] Formatting integers in pandas dataframe

I've read the documentation and simply cannot understand why I can't seem to achieve my objective.

All I want to do is output integers with a thousands separator where appropriate.

I'm loading a spreadsheet from my local machine that is in the public domain here

Here's my MRE:

import pandas as pd

WORKBOOK = "/Volumes/Spare/Downloads/prize-june-2025.xlsx"

def my_formatter(v):
return f"{v:,d}" if isinstance(v, int) else v

df = pd.read_excel(WORKBOOK, header=2, usecols="B,C,E:H")
print(df.dtypes)
df.style.format(my_formatter)
print(df.head())


Output:

Prize Value int64
Winning Bond NO. object
Total V of Holding int64
Area object
Val of Bond int64
Dt of Pur datetime64[ns]
dtype: object
Prize Value Winning Bond NO. Total V of Holding Area Val of Bond Dt of Pur
0 1000000 103FE583469 50000 Stockport 5000 2005-11-29
1 1000000 352AC359547 50000 Edinburgh, City Of 5000 2019-02-11
2 100000 581WF624503 50000 Birmingham 20000 2024-06-03
3 100000 265SM364866 50000 Hertfordshire 32500 2016-01-31
4 100000 570HE759643 11000 Hertfordshire 11000 2024-02-22


I have determined that my_formatter() is never called and I have no idea why.

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