code: @Nullable
    PyExpr getVariableExpression(String variableName) {
      for (Map<String, PyExpr> frame : localVarExprs) {
        PyExpr translation = frame.get(variableName);
        if (translation != null) {
          return translation;
        }
      }
      return null;
    }
docs: Retrieves the Python expression for a given variable name. The stack is traversed from top to
  bottom, giving the tightest scope the highest priority.
  
  @param variableName The name of the variable.
  @return The translated expression, or null if not found.