bpo-31801: Enum: add _ignore_ as class option (#5237)

* bpo-31801:  Enum:  add _ignore_ as class option

_ignore_ is a list, or white-space seperated str, of names that will not
be candidates for members; these names, and _ignore_ itself, are removed
from the final class.

* bpo-31801:  Enum:  add documentation for _ignore_

* bpo-31801: Enum: remove trailing whitespace

* bpo-31801: Enum: fix bulleted list format

* bpo-31801: add version added for _ignore_

2 files changed, 52 insertions, 1 deletions

diff --git a/Lib/enum.py b/Lib/enum.py
index fe7cb20fc0..e5fe6f3b94 100644
--- a/Lib/enum.py
+++ b/Lib/enum.py
@@ -64,6 +64,7 @@ class _EnumDict(dict):
         super().__init__()
         self._member_names = []
         self._last_values = []
+        self._ignore = []
 
     def __setitem__(self, key, value):
         """Changes anything not dundered or not a descriptor.
@@ -77,17 +78,28 @@ class _EnumDict(dict):
         if _is_sunder(key):
             if key not in (
                     '_order_', '_create_pseudo_member_',
-                    '_generate_next_value_', '_missing_',
+                    '_generate_next_value_', '_missing_', '_ignore_',
                     ):
                 raise ValueError('_names_ are reserved for future Enum use')
             if key == '_generate_next_value_':
                 setattr(self, '_generate_next_value', value)
+            elif key == '_ignore_':
+                if isinstance(value, str):
+                    value = value.replace(',',' ').split()
+                else:
+                    value = list(value)
+                self._ignore = value
+                already = set(value) & set(self._member_names)
+                if already:
+                    raise ValueError('_ignore_ cannot specify already set names: %r' % (already, ))
         elif _is_dunder(key):
             if key == '__order__':
                 key = '_order_'
         elif key in self._member_names:
             # descriptor overwriting an enum?
             raise TypeError('Attempted to reuse key: %r' % key)
+        elif key in self._ignore:
+            pass
         elif not _is_descriptor(value):
             if key in self:
                 # enum overwriting a descriptor?
@@ -124,6 +136,12 @@ class EnumMeta(type):
         # cannot be mixed with other types (int, float, etc.) if it has an
         # inherited __new__ unless a new __new__ is defined (or the resulting
         # class will fail).
+        #
+        # remove any keys listed in _ignore_
+        classdict.setdefault('_ignore_', []).append('_ignore_')
+        ignore = classdict['_ignore_']
+        for key in ignore:
+            classdict.pop(key, None)
         member_type, first_enum = metacls._get_mixins_(bases)
         __new__, save_new, use_args = metacls._find_new_(classdict, member_type,
                                                         first_enum)
diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index e6324d4d8c..97559712b1 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -8,7 +8,12 @@ from enum import Enum, IntEnum, EnumMeta, Flag, IntFlag, unique, auto
 from io import StringIO
 from pickle import dumps, loads, PicklingError, HIGHEST_PROTOCOL
 from test import support
+from datetime import timedelta
 
+try:
+    import threading
+except ImportError:
+    threading = None
 
 # for pickle tests
 try:
@@ -1547,6 +1552,34 @@ class TestEnum(unittest.TestCase):
         self.assertEqual(round(Planet.EARTH.surface_gravity, 2), 9.80)
         self.assertEqual(Planet.EARTH.value, (5.976e+24, 6.37814e6))
 
+    def test_ignore(self):
+        class Period(timedelta, Enum):
+            '''
+            different lengths of time
+            '''
+            def __new__(cls, value, period):
+                obj = timedelta.__new__(cls, value)
+                obj._value_ = value
+                obj.period = period
+                return obj
+            _ignore_ = 'Period i'
+            Period = vars()
+            for i in range(13):
+                Period['month_%d' % i] = i*30, 'month'
+            for i in range(53):
+                Period['week_%d' % i] = i*7, 'week'
+            for i in range(32):
+                Period['day_%d' % i] = i, 'day'
+            OneDay = day_1
+            OneWeek = week_1
+            OneMonth = month_1
+        self.assertFalse(hasattr(Period, '_ignore_'))
+        self.assertFalse(hasattr(Period, 'Period'))
+        self.assertFalse(hasattr(Period, 'i'))
+        self.assertTrue(isinstance(Period.day_1, timedelta))
+        self.assertTrue(Period.month_1 is Period.day_30)
+        self.assertTrue(Period.week_4 is Period.day_28)
+
     def test_nonhash_value(self):
         class AutoNumberInAList(Enum):
             def __new__(cls):