Unsupported Locale Error with upgrading to Python 3.12 image from Python 3.10/11

[agosmou]

Description:

Bug/missing-packages with locale configuration in the AWS Lambda Python 3.12 runtime Docker images

Steps to reproduce:

✅ Working Condition:

Use a Python 3.10 image, then build and run your dockerfile as below:

# any of these 3.10 images work
FROM public.ecr.aws/lambda/python:3.10.2025.01.15.17-x86_64
# FROM public.ecr.aws/lambda/python:3.10.2025.01.15.17-arm64

ENTRYPOINT ["python", "-c", "\
import locale; \
print('Before setting locales:', locale.getlocale()); \
locale.setlocale(locale.LC_ALL, 'en_US.UTF-8'); \
print('After setting to en_US.UTF-8:', locale.getlocale()); \
locale.setlocale(locale.LC_ALL, 'es_ES.UTF-8'); \
print('After setting to es_ES.UTF-8:', locale.getlocale())"]

Run in your terminal:

docker build -t test . && docker run --rm test

Note the output:

Before setting locales: ('en_US', 'UTF-8')
After setting to en_US.UTF-8: ('en_US', 'UTF-8')
After setting to es_ES.UTF-8: ('es_ES', 'UTF-8')

❌ Broken Condition:

Replicate the above but use a Python 3.12 image.
Either:

FROM public.ecr.aws/lambda/python:3.12.2025.01.24.11-x86_64

or

FROM public.ecr.aws/lambda/python:3.12.2025.01.24.11-arm64

Observe the error output stating the locale setting is unsupported.

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/var/lang/lib/python3.12/locale.py", line 615, in setlocale
    return _setlocale(category, locale)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
locale.Error: unsupported locale setting
Before setting locales: ('C', 'UTF-8')

🩹 This can be addressed by modifying the Dockerfile so that your final Dockerfile looks like:

# these 3.12 images only work if I include the RUN and ENV lines below
FROM public.ecr.aws/lambda/python:3.12.2025.01.24.11-x86_64
# FROM public.ecr.aws/lambda/python:3.12.2025.01.24.11-arm64

RUN dnf install -y glibc-langpack-en glibc-langpack-es && dnf clean all

ENTRYPOINT ["python", "-c", "\
import locale; \
print('Before setting locales:', locale.getlocale()); \
locale.setlocale(locale.LC_ALL, 'en_US.UTF-8'); \
print('After setting to en_US.UTF-8:', locale.getlocale()); \
locale.setlocale(locale.LC_ALL, 'es_ES.UTF-8'); \
print('After setting to es_ES.UTF-8:', locale.getlocale())"]

satisfactory output:

Before setting locales: ('en_US', 'UTF-8')
After setting to en_US.UTF-8: ('en_US', 'UTF-8')
After setting to es_ES.UTF-8: ('es_ES', 'UTF-8')

---

⚠️ Is there a known issue with locale configuration in the AWS Lambda Python 3.12 runtime images❓

[agosmou]

probably also applied to 3.13