Python upgrades: choose the interpreter, then deal with removed modules and compiled packages

An interpreter change has three parts

Moving a Python application to a newer interpreter changes what the standard library contains, which prebuilt packages your dependencies can install, and which of your dependencies still support you at all. A version string in a Dockerfile is the smallest part of that.

• Standard-library removals: your own code and your dependencies may import modules that no longer exist.
• Compiled packages: they are published for particular interpreter versions, so a new interpreter may need newer releases.
• Support: a dependency may have dropped the old interpreter or not yet added the new one.

What the Python project says today

The Python developer guide, checked on 11 October 2026, shows 3.9 as end of life since 31 October 2025 and 3.10 since 1 October 2026. Python 3.11 and later receive security fixes, 3.13 is scheduled for them until October 2029, and 3.14 is in bugfix status. The guide marks scheduled dates and says they may change. If you are on 3.9 or 3.10, you may stop at 3.11 or 3.12 as an interim step, but that buys less time than a later target.

• Re-check the page before you act; its dates are the project's to change.
• Ask your host or base-image provider for its own cut-off date.

What 3.12 and 3.13 take away

From 3.9 or 3.10 to 3.13, two sets of removals apply. Python 3.12 removed distutils, imp, asyncore, asynchat and smtpd, and stopped installing setuptools in new virtual environments. Python 3.13 removed the 19 modules of PEP 594, including cgi, crypt, pipes and telnetlib, and lib2to3. Code that imports any of them fails on import, not at startup of the interpreter, so a test run that never reaches that file passes.

• Search your own code and dependencies for the removed module names.
• Import every module of the application once on the new interpreter.
• A framework major version is a separate job; Django 1.11 on Python 2.7 has its own job.

Which job fits

An application on Python 3.9 or 3.10 with pinned dependencies and a runnable test command matches the fixed Python 3.13 job. Python 2 code needs a different assessment, and an app behind in several places benefits from an inventory first. Send the interpreter version, how packages are installed and which packages compile. Do not send environment files or customer data. Prices are untested proposals and payment follows the agreed checks.