Meta-ticket for Python 3.6+ preparation (sage library) - stage 2

[wluebbe]

For progress on making all doctests pass, see #26212

This meta-ticket tracks those tickets for changing the Sage library that did not go into stage 1 (ticket:15980).

Some reasons for assigning tasks to stage 2:

• The code can run on Python 2 only with the support of imported "compatibility" libraries. [copied from description] Maybe we have to check the licenses of the used compatibility libraries.
• The tasks are usually more complicated. The approach may not be obvious or uncontroversial.
• To make progress we need a Python 3.3 test environment for them.

This ticket is referenced by the meta-ticket ticket:15530

No.	2to3 fixer	see ticket	Comment
2	basestring	#16064	about 27 modules
5	dict	#15981	about 227 py modules
7	exec	#16065	6 modules
8	execfile	#16066	2 modules
17	imports	#16069	about 39 modules
22	itertools_import	#16070	about 12 modules
23	itertools	#16071	about 20 modules
24	long	#16072	about 72 modules
25	map	#16073	about 171 modules; (from future_builtins import map ?)
26	metaclass	#16074	about 30 modules
29	next	#18802	about 15 py modules
30	nonzero	#16076	about 25 modules
31	numliterals	#15987, #17808	oct and long literals
35b	raise traceback	#18799	about 3 py modules
36	raw_input	#16077	3 modules
46	unicode	#16079, #14153	lots of modules? (from __future__ import unicode_literals ?)
47	urllib	#16080	about 16 modules
49	xrange	#16081	about 293 modules changes
51	zip	#16082	Fixed (kept as a watchdog ticket)

The following changes do not relate to 2to3:

71	type()	#16085	about 161 modules; different values of type()function
72	write()	#16086	about 79 modules; in Py3 the write() function has a return value
73	traceback	#16088	about ?? modules; tracebacks can look different
74	file-to-open	#16097	about 20 modules; replace builtin file() by open()

[wluebbe]

Moved ticket:15981 (fix_dict) to stage 2.

[wluebbe]

Moved ticket:15987 (fix_literals) to stage 2.

[ppurka]

Is it true that this stage 2 depends on the modifications already made to stage 1? Then perhaps we should put #15980 in the dependencies field of the ticket.

[wluebbe]

Stage 2 does not depend on stage 1. The tickets of stage 1 could be solved after stage 2 tickets. They are usually improvements of Py2 code (without relying on separate "compatibility layer").

Both stage 1 and stage 2 are tracked as dependencies of the meta-ticket ticket:15530.

[wluebbe]

Moved ticket:16067 and ticket:16078 to stage 1 (meta ticket:15980).