@Override
    protected void addCompletions(@NotNull final CompletionParameters parameters,
                                  @NotNull final ProcessingContext context,
                                  @NotNull CompletionResultSet result) {
      final PsiElement original = parameters.getOriginalPosition();
      if (original != null) {
        final PsiElement parent = original.getParent();
        result = result.withPrefixMatcher(getPrefix(parameters.getOffset(), parent.getContainingFile()));

        if (parent instanceof PyStringLiteralExpression) {
          result.addAllElements(addCompletionsForSubstitutions(parameters, original, (PyStringLiteralExpression)parent));
        }
      }
    }
@Override
    protected void addCompletions(@NotNull final CompletionParameters parameters,
                                  @NotNull final ProcessingContext context,
                                  @NotNull CompletionResultSet result)