The range() object is immutable, but is not atomic, and copy.deepcopy() shouldn't return it unchanged.

>>> class I(int): pass  # mutable index
... 
>>> import copy
>>> r = range(I(10))
>>> r2 = copy.deepcopy(r)
>>> r.stop.attr = 'spam'
>>> r2.stop.attr
'spam'

This is Python 3 only issue because in 2.7 the xrange() object doesn't exposes start/stop/step attributes.

Proposed patch fixes the copy module.

Hum ok, it's a bug :-) It should be fixed. Do you want to work on a patch?

I don't have much experience with the copy module, but I don't see any problems with the code.

Does copy.copy suffer from the same problem?  If yes, is it fixed with this same patch, or is more work needed?

Victor, patch was already attached.  ;)

deepcopy_range.patch looks good to me.

Returning the same range() object from copy.copy() is correct. This is shallow copying.

New changeset 5772eae17a82 by Serhiy Storchaka in branch '3.5':
Issue #26202: copy.deepcopy() now correctly copies range() objects with
https://hg.python.org/cpython/rev/5772eae17a82

New changeset d5d0b62c2830 by Serhiy Storchaka in branch 'default':
Issue #26202: copy.deepcopy() now correctly copies range() objects with
https://hg.python.org/cpython/rev/d5d0b62c2830

Thanks Victor.

New changeset 5f4b229df7812f1788287095eb6b138bb21876a4 by Serhiy Storchaka in branch 'master':
bpo-40792: Make the result of PyNumber_Index() always having exact type int. (GH-20443)
https://github.com/python/cpython/commit/5f4b229df7812f1788287095eb6b138bb21876a4

This change has been reverted in issue40792. The range object attributes has now exact type int, so the original issue with deep copying is gone.