@@ -26,7 +26,6 @@

 # - ``ERROR_ON_CLONE``

 # - ``FILES``

 # - ``OFFLINE``

-# - ``PIP_DOWNLOAD_CACHE``

 # - ``RECLONE``

 # - ``REQUIREMENTS_DIR``

 # - ``STACK_USER``

@@ -1555,8 +1554,7 @@ function get_python_exec_prefix {

 }

 # Wrapper for ``pip install`` to set cache and proxy environment variables

-# Uses globals ``OFFLINE``, ``PIP_DOWNLOAD_CACHE``,

-# ``TRACK_DEPENDS``, ``*_proxy``

+# Uses globals ``OFFLINE``, ``TRACK_DEPENDS``, ``*_proxy``

 # pip_install package [package ...]

 function pip_install {

     local xtrace=$(set +o | grep xtrace)

@@ -1581,8 +1579,15 @@ function pip_install {

         local sudo_pip="sudo -H"

     fi

+    local pip_version=$(python -c "import pip; \

+                        print(pip.__version__.strip('.')[0])")

+    if (( pip_version<6 )); then

+        die $LINENO "Currently installed pip version ${pip_version} does not" \

+            "meet minimum requirements (>=6)."

+    fi

+

     $xtrace

-    $sudo_pip PIP_DOWNLOAD_CACHE=${PIP_DOWNLOAD_CACHE:-/var/cache/pip} \

+    $sudo_pip \

         http_proxy=$http_proxy \

         https_proxy=$https_proxy \

         no_proxy=$no_proxy \

@@ -1593,7 +1598,7 @@ function pip_install {

     if [[ "$INSTALL_TESTONLY_PACKAGES" == "True" ]]; then

         local test_req="$@/test-requirements.txt"

         if [[ -e "$test_req" ]]; then

-            $sudo_pip PIP_DOWNLOAD_CACHE=${PIP_DOWNLOAD_CACHE:-/var/cache/pip} \

+            $sudo_pip \

                 http_proxy=$http_proxy \

                 https_proxy=$https_proxy \

                 no_proxy=$no_proxy \