There is no “list slice” class in the Python standard library (nor is one built-in). So, you do need a class, though it need not be big — especially if you’re content with a “readonly” and “compact” slice. E.g.:
import collections
class ROListSlice(collections.Sequence):
def __init__(self, alist, start, alen):
self.alist = alist
self.start = start
self.alen = alen
def __len__(self):
return self.alen
def adj(self, i):
if i<0: i += self.alen
return i + self.start
def __getitem__(self, i):
return self.alist[self.adj(i)]
This has some limitations (doesn’t support “slicing a slice”) but for most purposes might be OK.
To make this sequence r/w you need to add __setitem__
, __delitem__
, and insert
:
class ListSlice(ROListSlice):
def __setitem__(self, i, v):
self.alist[self.adj(i)] = v
def __delitem__(self, i, v):
del self.alist[self.adj(i)]
self.alen -= 1
def insert(self, i, v):
self.alist.insert(self.adj(i), v)
self.alen += 1