Merge pull request #15278 from matt-kwong/python-fallback

Remove the fallback when creating Python virtual env

templates/tools/dockerfile/test/python_jessie_x64/Dockerfile.template

@@ -19,6 +19,10 @@
   <%include file="../../apt_get_basic.include"/>
   <%include file="../../gcp_api_libraries.include"/>
   <%include file="../../python_deps.include"/>
+  # Install pip and virtualenv for Python 3.4
+  RUN curl https://bootstrap.pypa.io/get-pip.py | python3.4
+  RUN python3.4 -m pip install virtualenv
+
   <%include file="../../run_tests_addons.include"/>
   # Define the default command.
   CMD ["bash"]

tools/dockerfile/test/python_jessie_x64/Dockerfile

@@ -68,6 +68,10 @@ RUN pip install --upgrade pip==10.0.1
 RUN pip install virtualenv
 RUN pip install futures==2.2.0 enum34==1.0.4 protobuf==3.5.2.post1 six==1.10.0 twisted==17.5.0
 
+# Install pip and virtualenv for Python 3.4
+RUN curl https://bootstrap.pypa.io/get-pip.py | python3.4
+RUN python3.4 -m pip install virtualenv
+
 # Prepare ccache
 RUN ln -s /usr/bin/ccache /usr/local/bin/gcc
 RUN ln -s /usr/bin/ccache /usr/local/bin/g++

tools/run_tests/helper_scripts/build_python.sh

@@ -112,10 +112,6 @@ export CFLAGS="-I$ROOT/include -std=gnu99 -fno-wrapv $CFLAGS"
 export GRPC_PYTHON_BUILD_WITH_CYTHON=1
 export LANG=en_US.UTF-8
 
-# Default python on the host to fall back to when instantiating e.g. the
-# virtualenv.
-HOST_PYTHON=${HOST_PYTHON:-python}
-
 # If ccache is available on Linux, use it.
 if [ "$(is_linux)" ]; then
   # We're not on Darwin (Mac OS X)
@@ -132,14 +128,9 @@ fi
 # Perform build operations #
 ############################
 
-# Instantiate the virtualenv, preferring to do so from the relevant python
-# version. Even if these commands fail (e.g. on Windows due to name conflicts)
-# it's possible that the virtualenv is still usable and we trust the tester to
-# be able to 'figure it out' instead of us e.g. doing potentially expensive and
-# unnecessary error recovery by `rm -rf`ing the virtualenv.
-($PYTHON -m virtualenv "$VENV" ||
- $HOST_PYTHON -m virtualenv -p "$PYTHON" "$VENV" ||
- true)
+# Instantiate the virtualenv from the Python version passed in.
+$PYTHON -m pip install virtualenv
+$PYTHON -m virtualenv "$VENV"
 VENV_PYTHON=$(script_realpath "$VENV/$VENV_RELATIVE_PYTHON")
 
 # See https://github.com/grpc/grpc/issues/14815 for more context. We cannot rely