The len() function is a built-in function in Python, meaning it's readily available without needing to import any external modules. Its primary purpose is to return the number of items in an object.

之前提到len函数式会调用对象的__len__, 如果是使用遍历的方式求长度那么效率会很低, 但是在求python内置类型的长度比如len(list ...