python-stdlib/enum/enum.py: Add Enum class. by IhorNehrutsa · Pull Request #980 · micropython/micropython-lib

IhorNehrutsa · 2025-03-05T10:29:25Z

Docs in:
docs/library/enum.rst: Add Enum class. #16842
Usage example:

from enum import Enum

class Color(Enum):
    RED = 'red'
    GREEN = 'green'

# Initialize the enum to process attributes
c = Color()

print(c.RED)        # Output: RED: red
print(c.RED.name)   # Output: RED
print(c.RED.value)  # Output: red
print(c.RED())      # Output: red

EDITED:
Inspired by @shariltumin Dot class from the Way to use dot notation to refer to states in a state machine #15694
and @njourdane enum() func from the Request for package: micropython-enum #269

EDITED April 2026:
Gemini-based version of enum.py and unit test test_enum.py

Code size report:
esp32: +1552 +0.088% ESP32_GENERIC[incl +1552(data)]
mimxrt: +1496 +0.380% TEENSY40
rp2: +1508 +0.163% RPI_PICO_W
samd: +1512 +0.545% ADAFRUIT_ITSYBITSY_M4_EXPRESS

IhorNehrutsa · 2025-03-05T13:08:03Z

Usage example::

from enum import Enum

class State(Enum):
  Stop = 10
  Run = 20
  Ready = 30

state = State()
print("state:", State())

current_state = state.Stop
print("current_state:", current_state, current_state.name)
if current_state == state.Stop:
  print(" Stop state")
if current_state != state.Ready:
  print(" Not a Ready state")
  print(" Run!")
  current_state = state.Run
print("current_state:", current_state, current_state.name)
# some process
i = -1
while current_state != state.Ready:
  i += 1
  if state.is_value(i):
      if state(i) == state.Ready:
          current_state = state.Ready
  print(".", end="")
print()
print("current_state:", current_state, state(current_state))
print("Done!")

Output is::

state: State(names={'Run': 20, 'Stop': 10, 'Ready': 30})
current_state: Stop: 10 Stop
 Stop state
 Not a Ready state
 Run!
current_state: Run: 20 Run
...............................
current_state: Ready: 30 Ready: 30
Done!

dpgeorge · 2025-03-11T00:53:53Z

Thanks for the contribution, this looks pretty good!

Did you implement this from scratch, or copy parts from CPython's implementation? I'm just wondering about licensing and copyright.

Can you please add the test to the CI, in tools/ci.sh inside the function ci_package_tests_run.

IhorNehrutsa · 2025-03-11T07:47:32Z

Did you implement this from scratch, or copy parts from CPython's implementation?

I just saw CPython Enum. It looks like incredible magic. :-)

dpgeorge · 2025-03-11T11:28:22Z

I just saw CPython Enum. It looks like incredible magic. :-)

That doesn't really answer the question. Did you copy this implementation from CPython?

Also, please make sure the CI all passes, there's currently a failure.

IhorNehrutsa · 2025-03-11T11:35:41Z

| Did you implement this from scratch, or copy parts from CPython's implementation?

No, I didn't use CPython implementation.

It was inspired by @shariltumin Dot class from the Way to use dot notation to refer to states in a state machine #15694
and @njourdane enum() func from the Request for package: micropython-enum #269

IhorNehrutsa · 2025-03-12T07:38:19Z

Should I squash commits?

dpgeorge · 2025-04-10T06:12:35Z

@@ -0,0 +1,91 @@
+# enum_test.py
+
+from enum import Enum, enum


I tried to run this test under CPython 3.12.2 but it doesn't work, for many reasons. And it should run under CPython so we can test that the implementation of MicroPython's enum matches the CPython enum.

For example, enum does not exist in the enum CPython module. Which version of CPython were you testing against?

dpgeorge · 2025-04-10T06:12:47Z

+    Enabled = True
+
+
+state = Enum()


CPython cannot create enums in this way.

dpgeorge · 2025-04-10T06:12:58Z

+
+state = Enum()
+print(state)
+state = Direction()


CPython requires a value in the constructor here.

dpgeorge · 2025-04-10T06:13:26Z

+print(state)
+state = State()
+print(state)
+state = State({"X": 1.0, "Y": 2.0})


CPython doesn't allow such an argument to the constructor.

dpgeorge · 2025-04-10T06:14:35Z

+
+print("Direction(Direction.CCW):", Direction(Direction.CCW))
+print("Direction('CW'):", Direction("CW"))
+print("state(10):", state(10))


CPython doesn't allow calling an enum.

dpgeorge · 2025-04-10T06:15:19Z

+print("state('CW'):", state("CW"))
+print("type(state('CW')):", type(state("CW")))
+
+print("state.key_from_value(20):", state.key_from_value(20))


CPython doesn't have key_from_value().

dpgeorge · 2025-04-10T06:15:38Z

+    CCW = "CCW"
+
+
+class State(Direction):


CPython doesn't allow inheriting enums from each other.

dpgeorge · 2025-04-10T06:15:53Z

+print("type(state('CW')):", type(state("CW")))
+
+print("state.key_from_value(20):", state.key_from_value(20))
+print("len(state):", len(state))


CPython doesn't have __len__ on an enum.

dpgeorge · 2025-04-10T06:16:46Z

+
+print("state.keys():", state.keys())
+print("state.values():", state.values())
+print("state.items():", state.items())


CPython enums don't have keys/values/items methods.

jonnor · 2025-04-25T18:36:22Z

There is a quite comprehensive set of unit-tests for enum available in CPython: https://github.com/python/cpython/blob/main/Lib/test/test_enum.py
With some exceptions like the tests using inspect, threading, pickle it seems possible to port most of them to MicroPython. That would give a very high degree of confidence that the implementation is conformant. And in the cases that one chooses to not be conformant, that can be documented with skipped tests.

IhorNehrutsa · 2025-04-30T13:00:33Z

I have successfully completed the task that requires the Enum class.
I don't plan to support this PR in the future.
You are welcome to continue working with this PR as you wish.
Thanks everyone.

We need to mip install `datetime`, tzif-parser requires it. https://github.com/micropython/micropython-lib/tree/master/python-stdlib/datetime ``` mpremote connect id:a5f14b8bfbff4289 mip install datetime ``` ## CPython features originally used in `tzif-parser` which were missing or different in MicroPython * `sysconfig` * `enum` - micropython/micropython-lib#269 - micropython/micropython-lib#980 * Regex _named_ Groups - https://docs.python.org/3/howto/regex.html#non-capturing-and-named-groups - https://docs.micropython.org/en/latest/library/re.html * `dataclasses` - https://docs.python.org/3/library/dataclasses.html - https://github.com/orgs/micropython/discussions/13741 - https://github.com/dhrosa/udataclasses - https://udataclasses.readthedocs.io/en/latest/ * `struct` (https://docs.python.org/3/library/struct.html#format-characters) features not available in MicroPython (https://docs.micropython.org/en/latest/library/struct.html#module-struct): - `c` for `char`, which in CPython would be decoded as an instance of [`bytes`](https://docs.python.org/3/library/stdtypes.html#bytes-objects) with length 1. Instead of `c`, we could use `s`, but we know this is a single byte, so `b` does just fine, giving us a Python integer. The integral repeat count prefix `1` is superfluous. * [MicroPython `bytearray`](https://www.fredscave.com/43-micropython-data-types-bytearray.html) type doesn't have the [`clear()`](https://docs.python.org/3/library/stdtypes.html#sequence.clear) method [mutable sequences](https://docs.python.org/3/library/stdtypes.html#typesseq-mutable) in CPython do * `Typing.IO` - python/typing#829

mchobby · 2026-04-11T22:09:34Z

@dpgeorge
This PR looks stuck in time. I didn't find enum.py in micropython-lib/python-stdlib/enum.py .
Getting Enum for MicroPython would be really useful .

Need some help on this PR ? Were could I start ?

Dominique

Josverl · 2026-04-12T07:51:53Z

Need some help on this PR ? Were could I start ?

That would be much appreciated.
I would suggest that making it match Cpython more and changing/adding tests to prove that would be the next step

IhorNehrutsa · 2026-04-13T11:45:48Z

@mchobby @Josverl You may pull down this PR and try to use enum.py. Please write reviews about usage here

Josverl · 2026-04-14T08:52:37Z

@IhorNehrutsa, may I ask why you closed the documentation PR?

IhorNehrutsa · 2026-04-14T10:03:52Z

@IhorNehrutsa, may I ask why you closed the documentation PR?

This has been going on for so long that I forgot. :(

mchobby · 2026-04-15T06:48:54Z

I'm a bit skeptical about the last @IhorNehrutsa action.
As I understand, the initial PR enum.py behavior was too far from CPython implementation.
I was interested to help in reducing the gap between CPython & MicroPython implementation.
That was looking as a "Good-First-Issue" to me (and for me).

On the meanwhile, @IhorNehrutsa pushed an AI rework of the code and "here is it for you to test".
As last arrival in this PR (and micropython-lib), I'm not in great position to evaluate the appropriateness of that rework.
@Josverl could you have a quick review on this for guidance?

Nevertheless, I do not want to be retrograde but being the "human behind the IA for checking the IA work" is not really what I was expecting.
Cheers

Josverl · 2026-04-15T09:09:18Z

@mchobby,
I agree with the earlier comments that it isn’t the reviewer’s job to try to interpret or “fix up” clearly AI‑generated submissions. If the submitter isn’t putting in at least the same level of effort as the reviewers, the process becomes unbalanced and unsustainable.
That does not mean that AI is not to be used as a tool to create code, but it does mean that there needs to be more that just that.

@IhorNehrutsa , I’m also genuinely confused by the pattern of behavior around these PRs: starting work, abandoning it, then suddenly re‑engaging with AI‑generated updates, along with the closing, and re‑opening of related PRs. It makes it difficult to understand the actual intent, the direction of the contribution, or whether you are committed to following through.
to be clear - I do appreciate your efforts, and I realize that sometimes the wait for a PR to get merged (or even rejected) can exceed ones attention span. but in order for us to work as a community I prefer to have some level confidence.

There is clear interest in having an Enum class available in MicroPython. But implementing one properly is non‑trivial — it touches (the lack of) metaclasses, memory constraints, and the broader philosophy of keeping the core minimal.

At the same time, it’s important that MicroPython stays close to CPython where feasible, while still respecting MicroPython’s own design principles and constraints. Achieving that balance requires careful design and discussion, not a surface‑level or (mostly) AI‑generated port.

I have not had the time to look at the most recent tests and code - but I do plan to do that in the next few days.

IhorNehrutsa · 2026-04-15T10:16:53Z

Okay. No one minds if I copy the previous version of enum.py to enum_0.py, the latest to enum_1.py, then we'll choose the best implementation options for enum.py from them.

IhorNehrutsa · 2026-04-15T10:24:10Z

There is a quite comprehensive set of unit-tests for enum available in CPython: https://github.com/python/cpython/blob/main/Lib/test/test_enum.py With some exceptions like the tests using inspect, threading, pickle it seems possible to port most of them to MicroPython. That would give a very high degree of confidence that the implementation is conformant. And in the cases that one chooses to not be conformant, that can be documented with skipped tests.

Can someone write a MicroPython version of the CPython tests https://github.com/python/cpython/blob/main/Lib/test/test_enum.py ?

mchobby · 2026-04-18T16:04:56Z

@dpgeorge
Use case
I'm currently porting almost achieved driver to MicroPython (source https://github.com/LukeYoung3000/Vishay_VCNL4035_Arduino/tree/master ).
This drivers contains lots of constant and enums definition (see https://github.com/LukeYoung3000/Vishay_VCNL4035_Arduino/blob/master/vcnl4035_Defs.h ).

I did implement the C enum as Python class (to stay close of original source code while porting and testing).

Example:

# Proximity Sensor Integration (T = 50 micro sec)
class VCNL4035_PS_IT:
        PS_IT_50us  = const(0) # 1.0 T
        PS_IT_75us  = const(1) # 1.5 T
        PS_IT_100us = const(2) # 2.0 T
        PS_IT_125us = const(3) # 2.5 T
        PS_IT_150us = const(4) # 3.0 T
        PS_IT_175us = const(5) # 3.5 T
        PS_IT_200us = const(6) # 4.0 T
        PS_IT_400us = const(7) # 8.0 T

Optimisation will comes later

Why using enum?
Using python enum just looks more appropriate.
I'm alway writing demonstration/test scripts for the target Hardware.
With enum script could retrieves the "name" of the current value to print it.
This would be definitively useful for debugging and testing.

mchobby · 2026-04-18T16:23:35Z

@dpgeorge , @IhorNehrutsa
I do agree with both of you each for a different reason. I have a suggestion.

As said @dpgeorge , if it is call Enum.py then it should work like CPython Enum. This is what common coder would expect.
As said @IhorNehrutsa , memory footprint is important and getting the main behavior would be sufficient (I think that Immutability should be preserved... to stay closer of enum).

Suggestion: name it AlmostEnum.py and document it properly. Having significant Enum behavior working on MicroPython and CPython would then acceptable as most of coder would use the main features.
The Memory footprint would stay low.
The Good practice should avoid the addition (and usage) of new features (not supported in Enum).

Regards,
Dominique

IhorNehrutsa · 2026-04-18T17:22:38Z

I don't sure about the const(). Try int values of enum. from enum import Enum class VCNL4035_PS_IT(Enum) : PS_IT_50us = 0 # 1.0 T PS_IT_75us = 1 # 1.5 T ..... See usage examples in the end of enum.py and in test_enum.py. Now Enum looks like CPython more then prev version

IhorNehrutsa · 2026-04-22T08:21:52Z

Why does nobody look at #1061?

Josverl · 2026-04-22T09:05:21Z

@IhorNehrutsa

Andrew has indicated that PR as Draft , and if you look at the implementation it states "This module requires metaclass support.". Metaclass is a rather complex core capability that is not currently part of MicroPython and that both he and I have been working on. Andrew's PR on that micropython/micropython#18416 uses less code than mine , but is still a significant growth.

TLDR; Behind that seemingly simple Enum hides a a rather complex machinery that comes at a cost.

and with that come choices - and weighing of options to compare features, compatibility and firmware sizes.
Perhaps it would be good to document different options and their pro/cons for discussion

IhorNehrutsa · 2026-04-23T18:18:23Z

Code size report:
esp32: +1968 +0.113% ESP32_GENERIC[incl +1968(data)]

IhorNehrutsa · 2026-04-24T11:07:25Z

Code size report:
esp32: +1712 +0.098% ESP32_GENERIC[incl +1712(data)]

IhorNehrutsa · 2026-04-27T11:43:44Z

Code size report:
esp32: +2688 +0.154% ESP32_GENERIC[incl +2688(data)]

Josverl · 2026-04-28T08:36:36Z

@IhorNehrutsa
I suggest to change the status of these PRs to Draft.
You appear to still be working through both the functionality offered as well as the code size -
You keep making regular updates - which is fine - setting the draft / would help let maintainers know when it is stable enough to spend more time reviewing it.

IhorNehrutsa · 2026-04-28T15:43:55Z

Code size report:
esp32: +1568 +0.090% ESP32_GENERIC[incl +1568(data)]

IhorNehrutsa · 2026-04-28T15:50:58Z

I think I've reached the maximum functionality and minimum code size. Right now, I'm missing feedback.

IhorNehrutsa · 2026-05-04T07:47:47Z

Code size report:
esp32: +1600 +0.092% ESP32_GENERIC[incl +1600(data)]
mimxrt: +1568 +0.407% TEENSY40
rp2: +1564 +0.170% RPI_PICO_W
samd: +1564 +0.569% ADAFRUIT_ITSYBITSY_M4_EXPRESS

IhorNehrutsa · 2026-05-07T06:38:49Z

Ready for review

IhorNehrutsa · 2026-05-27T09:44:35Z

Is there any feedback?

Josverl · 2026-05-27T20:52:47Z

One of the twenty-something post its on my MicroPython to-do list is to do a full review and comparison.

But I can't give you a date

agatti

I've had a quick look at the code, and whilst I'm still going through the internals of this module, I can at least provide a couple of hints on how to make the final output smaller :)

agatti · 2026-06-13T10:58:47Z

I believe this should be renamed into README.md.

agatti · 2026-06-13T10:58:58Z

+        if name and names:
+            # Support Functional API: Enum("Name", {"KEY1": VALUE1, "KEY2": VALUE2, ..})
+            # Dynamically create: class <name>
+            new_cls = type(name, (cls,), {"_inited": True})


If _inited isn't meant to be accessible from outside the instance, the name could be shortened to save some more space :)

agatti · 2026-06-13T10:59:10Z

+
+    def __setattr__(self, k, v):
+        if "_inited" in self.__class__.__dict__:
+            raise AttributeError(f"Enum '{self.__class__.__name__}' is immutable")


Exceptions usually start with a lower case letter, but I guess that in this case Enum indicates the class name.

Given that immutability seems to be something missing from the CPython implementation (unless I missed it in the documentation, that is!), we don't have to follow a set template. This string may be reduced to '{self.__class__.__name__}' is immutable, and still be useful.

agatti · 2026-06-13T10:59:15Z

+        super().__setattr__(k, v)
+
+    def __delattr__(self, k):
+        raise AttributeError("Enum is immutable")


If you reuse the same string as the one in __setattr__ it will just use the old string ID rather than creating a new string in the bytecode.

agatti · 2026-06-13T10:59:19Z

+        return self.list() == o.list()
+
+
+if __name__ == "__main__":


This section of the code gets compiled into bytecode too, so it's better if it's refactored into its own example file. Doing that saves 2657 bytes once the module is compiled.

This section was deleted in #16842 for code size check.
It will be removed from here after final review.

Thancks, Alessandro

IhorNehrutsa · 2026-06-15T07:56:39Z

Code size report:
esp32: +1552 +0.088% ESP32_GENERIC[incl +1552(data)]
mimxrt: +1496 +0.380% TEENSY40
rp2: +1508 +0.163% RPI_PICO_W
samd: +1512 +0.545% ADAFRUIT_ITSYBITSY_M4_EXPRESS

Signed-off-by: Ihor Nehrutsa <Ihor.Nehrutsa@gmail.com>

This was referenced Mar 5, 2025

docs/library/enum.rst: Add Enum class. micropython/micropython#16842

Open

Enum for micropython micropython/micropython#8545

Open

Request for package: micropython-enum #269

Open

IhorNehrutsa changed the title ~~Add Enum class.~~ python-stdlib/enum/enum.py: Add Enum class. Mar 5, 2025

Josverl reviewed Mar 11, 2025

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Josverl mentioned this pull request Oct 29, 2025

metaclass micropython/micropython#6094

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IhorNehrutsa force-pushed the enum branch from 6ab2ebe to 0ec8afd Compare April 13, 2026 10:43

IhorNehrutsa force-pushed the enum branch from fb0ac9a to 4ed3df9 Compare April 16, 2026 15:19

IhorNehrutsa requested a review from Josverl April 21, 2026 12:58

IhorNehrutsa force-pushed the enum branch from e9a3201 to 3e10d5b Compare April 22, 2026 07:52

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IhorNehrutsa requested a review from agatti June 15, 2026 08:10

python-stdlib\enum\enum.py: Add Enum class.

39b369c

Signed-off-by: Ihor Nehrutsa <Ihor.Nehrutsa@gmail.com>

IhorNehrutsa force-pushed the enum branch from 087f3cc to 39b369c Compare July 22, 2026 09:04

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