Python 3.15 RC2: check packages and UTF-8 safely before migrating

As of 15 September 2026. Python 3.15.0rc2 arrived on 1 September: a preview, not recommended for production. Python 3.15.0rc2 (2026-09-01) The final release is planned for 1 October, not guaranteed. PEP 790 Developers and small IT teams can use this period to prepare their scripts with copied data. This is a proposed checking procedure, not a software test we performed.

What to check

Python 3.15 enables UTF-8 mode by default. PEP 686 Pay particular attention to CSV imports, accented text and external program output. Updating Python does not automatically convert a file. Our recommendation is to compare real workflows using test copies, not merely check whether the application starts.

Requirements and boundaries

You need a separately installed, trusted Python 3.15 test interpreter, a project copy and documented dependencies. Match the intended operating system, architecture and interpreter variant. Do not replace system Python or the production environment. A venv separates Python packages Python: venv, but is not a security sandbox: test code must not reach production accounts, databases or message-delivery services. Use only approved packages and non-confidential test data.

Six steps in a test project

  1. Record the baseline: note the existing Python version, project revision, package versions and expected results. Back up source code and input files outside the new environment; retain the working installation.

  2. Confirm the interpreter: run the appropriate version command below. Expect the deliberately selected 3.15 test version, 3.15.0rc2 at this date. If the output differs, resolve the installation path before proceeding.

  3. Create a fresh environment: work inside the project copy and use a .venv315 directory that does not already exist. Then invoke its interpreter explicitly. Activation or a PowerShell execution-policy change is unnecessary.

  4. Install dependencies: follow the project's existing installation process. The commands below assume a reviewed requirements.txt; use the existing project tool for other lock formats. pip check checks dependency consistency pip check, not application behaviour.

  5. Compare functions: run existing tests and a representative import/export operation on copies. Compare row counts, special characters, amounts and output files against the previous environment. A successful launch is not enough.

  6. Record findings: retain the interpreter path, version, package set and reproducible steps. Distinguish missing packages, installation failures and changed results. Remove private paths and data from public issue reports.

Commands for the separate environment

Use only the block for your system. These commands do not install Python; they require the previously verified interpreter. Package installation downloads and installs project dependencies from configured sources. Run it only in the approved test project. pip install

Linux / macOS

python3.15 --version
python3.15 -m venv .venv315
.venv315/bin/python --version
.venv315/bin/python -m pip install -r requirements.txt
.venv315/bin/python -m pip check

Windows / PowerShell

py -3.15 --version
py -3.15 -m venv .venv315
.\.venv315\Scripts\python.exe --version
.\.venv315\Scripts\python.exe -m pip install -r requirements.txt
.\.venv315\Scripts\python.exe -m pip check

Assess results and return safely

Success means the intended interpreter, successful package installation, no reported dependency conflicts and matching business results. If pip finds no matching candidate, check the package version, supported Python versions, platform and approved package source. This does not automatically prove a Python bug; do not force installation by disabling checks. For garbled text or UnicodeError, establish the actual file encoding and specify it explicitly in the application. Do not label every legacy file UTF-8 or overwrite originals.

If problems appear, stop the test and continue with the unchanged previous environment. Keep the project copy and logs for diagnosis. A production decision later requires the final release and fresh application tests; a successful RC test does not replace them.

Sources and transparency

Source-based editorial guidance, without our own compatibility test or benchmark. No affiliate links or buying recommendation. Timeliness comes from the release-candidate phase; we claim no general search boom.