Multistage docker build

FROM python:3.9.6-slim-buster
# I create venv outside the workdir
# so even if we mount local folder to docker
# it won't be affected.
RUN python3 -m venv /opt/.venv
# ensure that virtualenv will be active
ENV PATH="/opt/.venv/bin:$PATH"

RUN apt-get update && \
    apt-get upgrade -y && \
    apt-get -y install --no-install-recommends libpq-dev build-essential && \
    rm -rf /var/lib/apt/lists/*

# Install dependencies:
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY main.py .
CMD ["python", "main.py"]

import psycopg2

# Connect to your postgres DB
conn = psycopg2.connect(dbname="test",
                        user="postgres",
                        password="secret",
                        host="db")

# Open a cursor to perform database operations
cur = conn.cursor()
cur.execute("SELECT now();")

psycopg2==2.9.1

FROM python:3.9.6-slim-buster AS build-base
RUN python3 -m venv /opt/.venv
# ensure that virtualenv will be active
ENV PATH="/opt/.venv/bin:$PATH"

RUN apt-get update && \
    apt-get upgrade -y && \
    apt-get -y install --no-install-recommends libpq-dev build-essential && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

# Install dependencies:
COPY requirements.txt .
RUN pip install -r requirements.txt

FROM python:3.9.6-slim-buster AS release
WORKDIR /code/
ENV PATH="/opt/.venv/bin:$PATH"
# Copy only virtualenv with all packages
COPY --from=build-base /opt/.venv /opt/.venv
# Run the application:
COPY main.py .
CMD ["python", "main.py"]

import stat
import subprocess
import sys
from pathlib import Path
from typing import List, Optional, Generator

EXECUTABLE_PERMISSIONS = stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH

def is_executable(filepath: Path) -> bool:
    return bool(filepath.stat().st_mode & EXECUTABLE_PERMISSIONS)

def find_all_executable_or_so_libs(venv_dir: Path) -> List[Path]:
    executable_files = set()
    for f in venv_dir.rglob('*'):
        if f.is_dir():
            continue
        if f.name.endswith('.so') or is_executable(f):
            executable_files.add(f)
    return sorted(list(executable_files))

def extract_lib_paths(dynamic_str: bytes) -> Optional[str]:
    """

    >>> extract_lib_paths(b"linux-vdso.so.1 (0x00007ffee695e000)")

    >>> extract_lib_paths(b"libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f1475154000)")
    '/usr/lib/libpthread.so.0'
    >>> extract_lib_paths(b"libpthread.so.0 => libpthread.so.0 (0x00007f1475154000)")

    """
    if b'=>' not in dynamic_str:
        return
    decoded_path = dynamic_str.decode(encoding='utf-8').strip()
    dyn_lib_path = decoded_path.split()[2].strip()
    if '/' not in dyn_lib_path:
        return
    return dyn_lib_path


def find_linked_libs(filepaths: List[Path]) -> List[str]:
    result = set()
    for interesting_file in filepaths:
        p = subprocess.Popen(['ldd', interesting_file.absolute()], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        for ln in p.stdout:
            lib_path = extract_lib_paths(ln)
            if lib_path:
                result.add(lib_path)
    return sorted(list(result))


def who_owns_debian(lib_path: str) -> Generator[str, None, None]:
    p = subprocess.Popen(['dpkg', '-S', lib_path], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    lines = p.stdout.readlines()
    for line in lines:
        line = line.decode('utf-8')
        if '/' in line and ':' in line:
            package_name = line.split(':')[0]
            yield package_name


def collect_package_names_debian(shared_libs_paths: List[str]):
    total_names = set()
    for one_lib_path in shared_libs_paths:
        for pkg_name in who_owns_debian(one_lib_path):
            total_names.add(pkg_name) if pkg_name else None
    return sorted(list(total_names))

def main(source_dir):
    source_dir = Path(source_dir)
    interesting_files = find_all_executable_or_so_libs(source_dir)
    shared_libs = find_linked_libs(interesting_files)
    all_names = collect_package_names_debian(shared_libs)
    for name in all_names:
        print(name)


if __name__ == '__main__':
    main(sys.argv[1])

COPY requirements.txt .
RUN pip install -r requirements.txt
COPY find_deps.py find_deps.py
RUN python find_deps.py $VIRTUAL_ENV

FROM python:3.9.6-slim-buster AS build-base
ENV VIRTUAL_ENV=/opt/.venv
RUN python3 -m venv $VIRTUAL_ENV
# ensure that virtualenv will be active
ENV PATH="$VIRTUAL_ENV/bin:$PATH"

RUN apt-get update && \
    apt-get upgrade -y && \
    apt-get -y install --no-install-recommends libpq-dev build-essential && \
    rm -rf /var/lib/apt/lists/*

# Install dependencies:
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY find_deps.py find_deps.py
RUN python find_deps.py $VIRTUAL_ENV

FROM python:3.9.6-slim-buster AS release
WORKDIR /code/
ENV PATH="/opt/.venv/bin:$PATH"
# install system dependencies
RUN apt-get update && \
    apt-get upgrade -y && \
    apt-get -y install --no-install-recommends libpq5 && \
    rm -rf /var/lib/apt/lists/*

COPY --from=build-base /opt/.venv /opt/.venv
# Run the application:
COPY main.py .
CMD ["python", "main.py"]