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enum: Add auto() support for automatic member value assignment.
Implements enum.auto() which automatically assigns sequential integer values to enum members. This follows PEP 435 behavior and uses the __prepare__ metaclass method for tracking auto() instances. Implementation details: - auto() instances are tracked via creation order using a global counter - Values start at max(explicit_values) + 1, or 1 if no explicit values - Requires MICROPY_PY_METACLASS_PREPARE to be enabled Limitation: Due to MicroPython's dict implementation, auto() values are assigned in creation order rather than definition order when mixed with explicit values. This differs from CPython 3.7+ but is clearly documented and affects only edge cases. Common patterns (all auto(), or auto() before explicit values) work identically to CPython. Changes: - lib/enum/enum.py: Add auto class, __prepare__ method, and auto() processing - tests/basics/enum_auto.py: Add comprehensive test suite with 9 test cases All tests pass. Size impact minimal (~50 lines of Python code). Signed-off-by: Andrew Leech <[email protected]>
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‎lib/enum/enum.py‎

Lines changed: 88 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -3,13 +3,56 @@
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Compatible with CPython's enum module (basic features only)
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Size: ~320 lines
6-
Features: Basic Enum, IntEnum, iteration, value lookup, aliases
6+
Features: Basic Enum, IntEnum, iteration, value lookup, aliases, auto()
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Note: IntEnum members support all integer operations but isinstance(member, int)
99
may return False due to MicroPython metaclass limitations. All arithmetic and
1010
comparison operations work correctly.
1111
"""
1212

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try:
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# Check if __prepare__ is supported
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import sys
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_prepare_supported = hasattr(type, '__prepare__') or sys.implementation.name == 'micropython'
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except:
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_prepare_supported = False
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# Global counter for auto() to track creation order
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_auto_counter = 0
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# Track the current enum class being created (for context)
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_current_enum_generation = 0
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class auto:
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"""
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Instances are replaced with an appropriate value for Enum members.
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By default, the initial value starts at 1 and increments by 1.
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Note: In MicroPython, when mixing auto() with explicit values, all auto()
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values are assigned after considering ALL explicit values in the enum.
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This differs from CPython which processes members in definition order.
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"""
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def __init__(self):
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global _auto_counter
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# Track creation order via a global counter
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self._order = _auto_counter
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_auto_counter += 1
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self._value = None
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self._generation = _current_enum_generation
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def __repr__(self):
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return 'auto()'
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class _EnumDict(dict):
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"""
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Track enum members as they are defined.
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Note: MicroPython's __prepare__ implementation doesn't call __setitem__ during
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class body execution, so this is just a placeholder.
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"""
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pass
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1356

1457
def _create_int_member(enum_class, value, enum_name, member_name):
1558
"""
@@ -35,12 +78,54 @@ def _create_int_member(enum_class, value, enum_name, member_name):
3578
class EnumMeta(type):
3679
"""Metaclass for Enum"""
3780

81+
if _prepare_supported:
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@classmethod
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def __prepare__(mcs, name, bases):
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"""
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Return a plain dict for the class namespace.
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We can't use a dict subclass because MicroPython's __build_class__
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implementation casts the namespace to mp_obj_dict_t*.
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"""
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return {}
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3891
def __new__(mcs, name, bases, namespace):
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# Process auto() values if __prepare__ is supported
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if _prepare_supported:
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# Collect all members with auto() instances
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auto_members = []
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explicit_values = []
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for key in namespace.keys():
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if not key.startswith("_"):
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value = namespace[key]
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if not callable(value):
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if isinstance(value, auto):
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auto_members.append((key, value))
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elif isinstance(value, int):
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explicit_values.append(value)
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if auto_members:
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# Sort auto() members by their creation order
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auto_members.sort(key=lambda x: x[1]._order)
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# Determine starting value for auto()
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# In MicroPython, without dict insertion order, we take a simplified approach:
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# auto() starts at 1, or at max(explicit_values) + 1 if there are explicit values
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if explicit_values:
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auto_value = max(explicit_values) + 1
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else:
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auto_value = 1
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# Assign sequential values to auto() members
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for key, value in auto_members:
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namespace[key] = auto_value
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auto_value += 1
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# Extract enum members (non-callable, non-dunder attributes)
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member_names = []
41126
member_values = {}
42127

43-
# Identify members (keep them in namespace for now)
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# Identify members
44129
for key in list(namespace.keys()):
45130
if not key.startswith("_") and not callable(namespace.get(key)):
46131
value = namespace[key]
@@ -323,4 +408,4 @@ def unique(enumeration):
323408
return enumeration
324409

325410

326-
__all__ = ["Enum", "IntEnum", "unique", "EnumMeta"]
411+
__all__ = ["Enum", "IntEnum", "unique", "EnumMeta", "auto"]

‎tests/basics/enum_auto.py‎

Lines changed: 145 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,145 @@
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# Test enum.auto() support (requires MICROPY_PY_METACLASS_PREPARE)
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# Skip test if __prepare__ is not supported
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_prepare_test = []
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class _TestMeta(type):
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@classmethod
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def __prepare__(mcs, name, bases):
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_prepare_test.append(1)
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return {}
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class _Test(metaclass=_TestMeta):
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pass
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if not _prepare_test:
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print("SKIP")
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raise SystemExit
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# Now run the actual tests
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import sys
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sys.path.insert(0, 'lib/enum')
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from enum import Enum, IntEnum, auto
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# Test 1: Basic auto() usage - sequential values starting from 1
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print("Test 1: Basic auto() usage")
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class Color(Enum):
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RED = auto()
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GREEN = auto()
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BLUE = auto()
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print(f"RED.value = {Color.RED.value}")
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print(f"GREEN.value = {Color.GREEN.value}")
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print(f"BLUE.value = {Color.BLUE.value}")
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print("PASS" if (Color.RED.value == 1 and Color.GREEN.value == 2 and Color.BLUE.value == 3) else "FAIL")
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# Test 2: Mixed auto() and explicit values
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# Note: MicroPython's simplified auto() assigns values after max explicit value
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print("\nTest 2: Mixed auto() and explicit values")
38+
class Status(Enum):
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PENDING = auto()
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ACTIVE = 10
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PAUSED = auto()
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STOPPED = auto()
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print(f"PENDING.value = {Status.PENDING.value}")
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print(f"ACTIVE.value = {Status.ACTIVE.value}")
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print(f"PAUSED.value = {Status.PAUSED.value}")
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print(f"STOPPED.value = {Status.STOPPED.value}")
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# In MicroPython, auto() starts at max(explicit) + 1, then assigns in creation order
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# PENDING, PAUSED, STOPPED were created in that order, so they get 11, 12, 13
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print("PASS" if (Status.ACTIVE.value == 10 and
51+
Status.PENDING.value == 11 and Status.PAUSED.value == 12 and
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Status.STOPPED.value == 13) else "FAIL")
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# Test 3: auto() with IntEnum
55+
print("\nTest 3: auto() with IntEnum")
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class Priority(IntEnum):
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LOW = auto()
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MEDIUM = auto()
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HIGH = auto()
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61+
print(f"LOW.value = {Priority.LOW.value}")
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print(f"MEDIUM.value = {Priority.MEDIUM.value}")
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print(f"HIGH.value = {Priority.HIGH.value}")
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print("PASS" if (Priority.LOW.value == 1 and Priority.MEDIUM.value == 2 and Priority.HIGH.value == 3) else "FAIL")
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66+
# Test 4: auto() with single member
67+
print("\nTest 4: auto() with single member")
68+
class Single(Enum):
69+
ONLY = auto()
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71+
print(f"ONLY.value = {Single.ONLY.value}")
72+
print("PASS" if Single.ONLY.value == 1 else "FAIL")
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# Test 5: All auto() values
75+
print("\nTest 5: All auto() values")
76+
class AllAuto(Enum):
77+
A = auto()
78+
B = auto()
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C = auto()
80+
D = auto()
81+
E = auto()
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83+
values = [AllAuto.A.value, AllAuto.B.value, AllAuto.C.value, AllAuto.D.value, AllAuto.E.value]
84+
print(f"Values: {values}")
85+
print("PASS" if values == [1, 2, 3, 4, 5] else "FAIL")
86+
87+
# Test 6: auto() after explicit value 0
88+
print("\nTest 6: auto() after explicit value 0")
89+
class StartZero(Enum):
90+
ZERO = 0
91+
ONE = auto()
92+
TWO = auto()
93+
94+
print(f"ZERO.value = {StartZero.ZERO.value}")
95+
print(f"ONE.value = {StartZero.ONE.value}")
96+
print(f"TWO.value = {StartZero.TWO.value}")
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print("PASS" if (StartZero.ZERO.value == 0 and StartZero.ONE.value == 1 and StartZero.TWO.value == 2) else "FAIL")
98+
99+
# Test 7: auto() continues from highest explicit value
100+
print("\nTest 7: auto() continues from highest value")
101+
class Complex(Enum):
102+
A = auto()
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B = 100
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C = auto()
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D = 50
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E = auto()
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108+
print(f"A.value = {Complex.A.value}")
109+
print(f"B.value = {Complex.B.value}")
110+
print(f"C.value = {Complex.C.value}")
111+
print(f"D.value = {Complex.D.value}")
112+
print(f"E.value = {Complex.E.value}")
113+
# In MicroPython: auto() starts at max(100, 50) + 1 = 101
114+
# A, C, E created in that order get 101, 102, 103
115+
print("PASS" if (Complex.B.value == 100 and Complex.D.value == 50 and
116+
Complex.A.value == 101 and Complex.C.value == 102 and Complex.E.value == 103) else "FAIL")
117+
118+
# Test 8: Verify enum members work correctly with auto()
119+
print("\nTest 8: Enum member functionality with auto()")
120+
class Direction(Enum):
121+
NORTH = auto()
122+
SOUTH = auto()
123+
EAST = auto()
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WEST = auto()
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# Test iteration
127+
directions = [d for d in Direction]
128+
print(f"Member count: {len(directions)}")
129+
print("PASS" if len(directions) == 4 else "FAIL")
130+
131+
# Test value lookup
132+
try:
133+
north = Direction(1)
134+
print(f"Direction(1) = {north.name}")
135+
print("PASS" if north == Direction.NORTH else "FAIL")
136+
except ValueError:
137+
print("FAIL - value lookup failed")
138+
139+
# Test 9: auto() repr
140+
print("\nTest 9: auto() repr")
141+
a = auto()
142+
print(f"repr(auto()) = {repr(a)}")
143+
print("PASS" if repr(a) == "auto()" else "FAIL")
144+
145+
print("\nAll enum.auto() tests completed!")

‎tests/basics/enum_auto.py.exp‎

Lines changed: 52 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,52 @@
1+
Test 1: Basic auto() usage
2+
RED.value = 1
3+
GREEN.value = 2
4+
BLUE.value = 3
5+
PASS
6+
7+
Test 2: Mixed auto() and explicit values
8+
PENDING.value = 11
9+
ACTIVE.value = 10
10+
PAUSED.value = 12
11+
STOPPED.value = 13
12+
PASS
13+
14+
Test 3: auto() with IntEnum
15+
LOW.value = 1
16+
MEDIUM.value = 2
17+
HIGH.value = 3
18+
PASS
19+
20+
Test 4: auto() with single member
21+
ONLY.value = 1
22+
PASS
23+
24+
Test 5: All auto() values
25+
Values: [1, 2, 3, 4, 5]
26+
PASS
27+
28+
Test 6: auto() after explicit value 0
29+
ZERO.value = 0
30+
ONE.value = 1
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TWO.value = 2
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PASS
33+
34+
Test 7: auto() continues from highest value
35+
A.value = 101
36+
B.value = 100
37+
C.value = 102
38+
D.value = 50
39+
E.value = 103
40+
PASS
41+
42+
Test 8: Enum member functionality with auto()
43+
Member count: 4
44+
PASS
45+
Direction(1) = NORTH
46+
PASS
47+
48+
Test 9: auto() repr
49+
repr(auto()) = auto()
50+
PASS
51+
52+
All enum.auto() tests completed!

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