很多Python函数或者类的方法中，帮助文档都显示最后有一个斜线，但是自己定义函数时却不允许这样用，请问这个斜线的作用是什么呢？
help(sum)
Help on built-in function sum in module builtins:
sum(iterable, start=0, /)
Return the sum of a 'start' value (default: 0) plus an iterable of numbers
When the iterable is empty, return the start value.
This function is intended specifically for use with numeric values and may
reject non-numeric types.
>>> help(id)
Help on built-in function id in module builtins:
id(obj, /)
Return the identity of an object.
This is guaranteed to be unique among simultaneously existing objects.
(CPython uses the object's memory address.)
help(input)
Help on built-in function input in module builtins:
input(prompt=None, /)
Read a string from standard input. The trailing newline is stripped.
The prompt string, if given, is printed to standard output without a
trailing newline before reading input.
If the user hits EOF (*nix: Ctrl-D, Windows: Ctrl-Z+Return), raise EOFError.
On *nix systems, readline is used if available.
>>> help(filter)
Help on class filter in module builtins:
class filter(object)
| filter(function or None, iterable) --> filter object
|
| Return an iterator yielding those items of iterable for which function(item)
| is true. If function is None, return the items that are true.
|
| Methods defined here:
|
| getattribute(self, name, /)
| Return getattr(self, name).
|
| iter(self, /)
| Implement iter(self).
|
| new(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
|
| next(self, /)
| Implement next(self).
|
| reduce(...)
| Return state information for pickling.
可变参数个数，后面可以跟任意个数的数字
已查找到正确答案，函数参数最后一个斜线表示该函数只接收位置参数而不接收关键参数，但是在Python中并不允许定义这样的函数，这样的函数一般是用C语言开发的内置函数或特定对象的方法，更加详细的资料可以查阅“Argument Clinic”有关资料。
斜线表示前面的参数必须以位置参数的形式进行传递，Python 3.8之后开始允许用户自定义函数中也进行这样的声明。
斜线表示该位置前面的所有参数必须以位置参数的形式进行传递，Python 3.8之前不允许用户自定义函数这样做，Python 3.8之后允许。