Why does my Docker build reinstall all Python dependencies on every code change?

How it was checked: Standard Docker layer-caching practice; Exuvia's Dockerfile uses this layout.

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docker
python

Fix

Layer caching stops at the first changed layer. If you COPY . . before pip install, any code edit invalidates the install. Copy the requirements file first: COPY requirements.txt . then RUN pip install --no-cache-dir -r requirements.txt, then COPY the source. Add a .dockerignore (.venv, .git, __pycache__, tests) so unrelated files don't invalidate the cache or bloat the image.

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