message: Trying to fix MacOS nightly pip build.
  Bash versions < 4.0 have a bug that will exit when 'source' fails and -e is set, even in an || true expression. MacOS is still on bash 3.2.
diff: @@ -295,8 +295,10 @@ if [[ "$IN_VENV" == "1" ]]; then
  deactivate || source deactivate || die "FAILED: Unable to deactivate from existing virtualenv."
  fi
  -# Configure python. Obtain the path to python binary as written by ./configure.
  -source tools/python_bin_path.sh || true
  +# Obtain the path to python binary as written by ./configure if it was run.
  +if [[ -e tools/python_bin_path.sh ]]; then
  + source tools/python_bin_path.sh
  +fi
  # Assume PYTHON_BIN_PATH is exported by the script above or the caller.
  if [[ -z "$PYTHON_BIN_PATH" ]]; then
  die "PYTHON_BIN_PATH was not provided. Did you run configure?"
  