Python Deployment

Detection

Project is Python if any of these exist:

Entry point files (checked in order): app.py, main.py, server.py, run.py, wsgi.py, asgi.py

Versions

Python version priority:

1. .python-version file or mise.toml / .tool-versions
2. pyproject.toml → [project].requires-python (e.g. >=3.11)
3. Pipfile → [requires].python_version
4. runtime.txt
5. Defaults to 3.13

Package Managers

Detect in order:

1. Lock files: poetry.lock → Poetry, pdm.lock → PDM, Pipfile.lock → Pipenv, uv.lock → uv
2. Manifest: pyproject.toml (poetry/pdm/uv) or Pipfile (pipenv) or requirements.txt (pip)
3. Default: pip with requirements.txt

Install Commands

Runtime Variables

Configure the Python runtime for production: enable the fault handler for crash diagnostics (PYTHONFAULTHANDLER=1), disable output buffering for real-time logs (PYTHONUNBUFFERED=1), randomize hash seeds (PYTHONHASHSEED=random), and skip bytecode generation (PYTHONDONTWRITEBYTECODE=1). Suppress pip version checks with PIP_DISABLE_PIP_VERSION_CHECK=1.

Build & Start

Start Command Resolution

1. Framework-specific (see below)
2. pyproject.toml → [project.scripts] or [tool.poetry.scripts]
3. setup.py → entry_points
4. manage.py → Django
5. Root entry files (first found): app.py, main.py, server.py, run.py → python <file>
6. Conventions: wsgi.py, asgi.py

Most Python web apps have no build step (interpreted).

Port Detection

1. PORT from .env or .env.example
2. Framework defaults:

Framework Detection

From dependencies in pyproject.toml, requirements.txt, or Pipfile:

Framework-Specific Start Commands

Flask — gunicorn <module>:app -b 0.0.0.0:${PORT:-5000} if gunicorn is a dependency, else flask run Django — python manage.py migrate && gunicorn <wsgi_module>:application -b 0.0.0.0:${PORT:-8000} --workers 2. Detect app from WSGI_APPLICATION in settings. FastAPI — uvicorn <module>:app --host 0.0.0.0 --port ${PORT:-8000} --workers 1 FastHTML — uvicorn <module>:app --host 0.0.0.0 --port ${PORT:-8000} Streamlit — streamlit run <entry>.py --server.port ${PORT:-8501} --server.address 0.0.0.0

System Dependencies

Install Stage Optimization

Copy pyproject.toml + lockfile first for layer caching, then full source.

Caching

Leverage BuildKit cache mounts to speed up rebuilds:

• pip: RUN --mount=type=cache,target=/root/.cache/pip pip install -r requirements.txt
• uv: RUN --mount=type=cache,target=/root/.cache/uv uv sync --frozen

Environment Variable Semantics

Dockerfile Patterns

uv (with lockfile)

FROM python:3.13-slim AS base

FROM base AS deps
WORKDIR /app
COPY pyproject.toml uv.lock ./
RUN pip install uv && uv sync --frozen

FROM base AS runtime
WORKDIR /app
ENV PYTHONUNBUFFERED=1 PYTHONDONTWRITEBYTECODE=1
COPY --from=deps /app/.venv /app/.venv
ENV PATH="/app/.venv/bin:$PATH"
COPY . .
EXPOSE 8000
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

pip + requirements.txt

FROM python:3.13-slim AS base

FROM base AS deps
WORKDIR /app
COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt

FROM base AS runtime
WORKDIR /app
ENV PYTHONUNBUFFERED=1 PYTHONDONTWRITEBYTECODE=1
COPY --from=deps /usr/local/lib/python3.13/site-packages /usr/local/lib/python3.13/site-packages
COPY . .
EXPOSE 8000
CMD ["gunicorn", "wsgi:app", "-b", "0.0.0.0:8000"]

Django with collectstatic

FROM python:3.13-slim AS base

FROM base AS deps
WORKDIR /app
COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt

FROM base AS build
WORKDIR /app
COPY --from=deps /usr/local/lib/python3.13/site-packages /usr/local/lib/python3.13/site-packages
COPY . .
ENV DJANGO_SETTINGS_MODULE=project.settings
RUN python manage.py collectstatic --noinput

FROM base AS runtime
WORKDIR /app
ENV PYTHONUNBUFFERED=1 PYTHONDONTWRITEBYTECODE=1
COPY --from=build /usr/local/lib/python3.13/site-packages /usr/local/lib/python3.13/site-packages
COPY --from=build /app/static /app/static
COPY --from=build /app /app
EXPOSE 8000
CMD ["gunicorn", "project.wsgi:application", "-b", "0.0.0.0:8000"]

Gotchas

• psycopg2 requires libpq-dev and gcc at build time — use psycopg2-binary instead to avoid native compilation
• uv --frozen fails if uv.lock doesn't exist — use uv sync without --frozen when no lockfile is present
• Django collectstatic needs DJANGO_SETTINGS_MODULE and may require a dummy SECRET_KEY at build time
• Poetry creates virtual environments outside the project by default — set POETRY_VIRTUALENVS_IN_PROJECT=true for Docker builds
• FastAPI/Uvicorn must bind to 0.0.0.0, not 127.0.0.1, to be reachable from outside the container
• Python site-packages path includes the minor version (e.g. python3.13) — the COPY path in multi-stage Dockerfiles must match the exact Python version