In python3, the help output for sorted, for example, is:
"sorted(iterable, /, *, key=None, reverse=False)"
What does the '/' and '*' mean?
help(sorted)
python2 output is
sorted(iterable, cmp=None, key=None, reverse=False) --> new sorted list
so what is the '/' and '*' in python3?
/ marks the end of positional-only parameters and the beginning of positional-or-keyword parameters, while * marks the end of positional-or-keyword parameters and the beginning of keyword-only parameters.
In case of the sorted function where the signature is sorted(iterable, /, *, key=None, reverse=False), it means that the iterable parameter can only be specified as a positional argument so you can't call sorted(iterable=some_list), and that the key and reverse parameters can only be specified as keyword arguments, so you can't call sorted(some_list, some_func, True).
Please refer to PEP-0457 for more details.