items = [1,2,3,4,5,6]

def do_something(*items):
    pass

>>> fstr = 'def f(%s): pass'%(', '.join(['arg%d'%i for i in range(5000)]))
>>> exec(fstr)
>>> f
<function f at 0x829bae4>

>>> exec 'f(' + ','.join(str(i) for i in range(5000)) + ')'

Traceback (most recent call last):
  File "<pyshell#63>", line 1, in <module>
    exec 'f(' + ','.join(str(i) for i in range(5000)) + ')'
  File "<string>", line 1
SyntaxError: more than 255 arguments (<string>, line 1)

>>> f(*range(5000))
>>>

if (nargs + nkeywords + ngens > 255) {
  ast_error(n, "more than 255 arguments");
  return NULL;
}