Put everything inside a venv

Dockerfile

@@ -5,12 +5,17 @@ FROM alpine:${ALPINE_VERSION}
 RUN apk add --no-cache git python3 python3-dev py3-pip py3-setuptools build-base
 
 # build wheels in first image
+ENV VIRTUAL_ENV /opt/venv
+ENV PATH ${VIRTUAL_ENV}/bin:${PATH}
+
+RUN python3 -m venv ${VIRTUAL_ENV}
+
 ADD . /tmp/src
 RUN cd /tmp/src && git clean -xfd && git status
 RUN mkdir /tmp/wheelhouse \
  && cd /tmp/wheelhouse \
- && pip3 install wheel \
- && pip3 wheel --no-cache-dir /tmp/src \
+ && pip install wheel \
+ && pip wheel --no-cache-dir /tmp/src \
  && ls -l /tmp/wheelhouse
 
 FROM alpine:${ALPINE_VERSION}
@@ -18,13 +23,18 @@ FROM alpine:${ALPINE_VERSION}
 # install python, git, bash, mercurial
 RUN apk add --no-cache git git-lfs python3 py3-pip py3-setuptools bash docker mercurial
 
+ENV VIRTUAL_ENV /opt/venv
+ENV PATH ${VIRTUAL_ENV}/bin:${PATH}
+
+RUN python3 -m venv ${VIRTUAL_ENV}
+
 # install hg-evolve (Mercurial extensions)
-RUN pip3 install hg-evolve --user --no-cache-dir
+RUN pip install hg-evolve --user --no-cache-dir
 
 # install repo2docker
 COPY --from=0 /tmp/wheelhouse /tmp/wheelhouse
-RUN pip3 install --no-cache-dir --ignore-installed --no-deps /tmp/wheelhouse/*.whl \
- && pip3 list
+RUN pip install --no-cache-dir --ignore-installed --no-deps /tmp/wheelhouse/*.whl \
+ && pip list
 
 # add git-credential helper
 COPY ./docker/git-credential-env /usr/local/bin/git-credential-env