Description
Pandas version checks
-
I have checked that this issue has not already been reported.
-
I have confirmed this bug exists on the latest version of pandas.
-
I have confirmed this bug exists on the main branch of pandas. (I am working on compiling and testing this.)
Reproducible Example
import pandas as pd
excel_file = "string_list.xlsx"
df_openpyxl = pd.read_excel(excel_file, engine="openpyxl")
df_calamine = pd.read_excel(excel_file, engine="calamine")
print("openpyxl engine")
print("===============")
print(df_openpyxl)
print("calamine engine")
print("===============")
print(df_calamine)
Issue Description
The attached excel file string_list.xlsx
contains the following data:
Header
0 Alone
1 Bone
2 None
3 Cone
4 Done
It looks like this:

When read with read_excel()
using either the openpyxl
or calamine
engine it converts the string cell "None" to a NaN
. The output from the above program is:
openpyxl engine
===============
Header
0 Alone
1 Bone
2 NaN
3 Cone
4 Done
calamine engine
===============
Header
0 Alone
1 Bone
2 NaN
3 Cone
4 Done
Note that "None" has changed to NaN
.
Sample file:
I checked openpyxl
, calamine
and python-calamine
outside of Pandas and they each print the expected string "None".
Expected Behavior
The string "None" from an Excel file shouldn't be interpreted as Python None
and/or converted to NaN
.
Installed Versions
INSTALLED VERSIONS
commit : 2cc3762
python : 3.11.1
python-bits : 64
OS : Darwin
OS-release : 24.5.0
Version : Darwin Kernel Version 24.5.0: Tue Apr 22 19:53:26 PDT 2025; root:xnu-11417.121.6~2/RELEASE_X86_64
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 2.3.0
numpy : 2.1.3
pytz : 2024.2
dateutil : 2.9.0.post0
pip : 25.1.1
Cython : None
sphinx : None
IPython : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : None
blosc : None
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : None
html5lib : None
hypothesis : None
gcsfs : None
jinja2 : 3.1.4
lxml.etree : None
matplotlib : None
numba : None
numexpr : None
odfpy : None
openpyxl : 3.1.5
pandas_gbq : None
psycopg2 : None
pymysql : None
pyarrow : 20.0.0
pyreadstat : None
pytest : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlsxwriter : 3.2.5
zstandard : None
tzdata : 2024.2
qtpy : None
pyqt5 : None