what is the meaning of / in the help function in python 3.5.1

Question

I have updated my python from 3.3.2 to 3.5.1 a few days ago, and the other day by doing help in some function I found something strange, a / in the firm of some of the functions, for example:

in 3.3.2

>>> help(len)
Help on built-in function len in module builtins:

len(...)
    len(object) -> integer

    Return the number of items of a sequence or mapping.

>>>

now in 3.5.1

>>> help(len)
Help on built-in function len in module builtins:

len(obj, /)
    Return the number of items in a container.

>>> 

what is the meaning of this /??

Answer 1

The slash means the end of the "positional only parameters", as better explained in this previous answer.