code: def select_by_ext(self, ext, recursive=True):
          
          ext = [ext.strip().lower() for ext in ensure_list(ext)]
  
          def filters(p): return p.suffix.lower() in ext
  
          return self.select_file(filters, recursive)
docs: Select file path by extension.
  
          :param ext:
  
          **中文文档**
  
          选择与预定义的若干个扩展名匹配的文件。