Python 3 planning

Which Python 3 version will be targeted? For instance, if f-strings are used, then this will preclude use by Py3 prior to 3.6.

Desired Python 3 features:

• use of nonlocal (3.0)
• except exceptiontype as var: (3.0)
• OrderedDict (3.1)
• autonumbered str.format {} placeholders (3.1)
• str.format_map (3.2)
• callable() builtin (3.2)
• yield from (3.3)
• raise Exception from None to abbreviate exception tracebacks (3.3)
• function __qualname__ (3.3)
• types.SimpleNamespace (3.3)
• ipaddress module (3.3)
• enum module (3.4)
• pathlib module (3.4)
• infix @ operator (3.5)
• typing module (3.5)
• collections.abc.Generator (3.5)
• f-strings (3.6)
• '_' in numeric literals and formats (3.6)
• __init_subclass__ (3.6)
• enum auto() numbering (3.6)
• functools.singledispatch (method signature overrides) (3.6)
• dataclasses (3.7)
• postponed annotation eval (future) (3.7)
• Forced UTF-8 runtime mode (3.7)
• breakpoint() builtin (3.7)
• module __getattr__
• contextlib.nullcontext() (3.7)

Conversion of examples?

• can be done any time, backward compatibility of examples is not a requirement
• if examples use a later Python feature, should use future import or do upfront Py version validation

Py2 compatibility code to be deleted:

• iterkeys, itervalues, iteritems in ParseResults
• _ustr()
• _MAX_INT
• import compatibility try-excepts
• unicode string literals (u"lskdjjf")
• __nonzero__
• super(type, self) -> just plain super()