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feat: sunder names in enum #2822

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merged 3 commits into from Mar 6, 2019

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@Hanaasagi
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commented Mar 3, 2019

This pull request wants to resolve #2766. Some details list here:

Python enum doc

Supported _sunder_ names

  • _name_ – name of the member
  • _value_ – value of the member; can be set / modified in __new__
  • _missing_ – a lookup function used when a value is not found; may be overridden
  • _ignore_ – a list of names, either as a list() or a str(), that will not be transformed into members, and will be removed from the final class
  • _order_ – used in Python 2/3 code to ensure member order is consistent (class attribute, removed during class creation)
  • _generate_next_value_ – used by the Functional API and by auto to get an appropriate value for an enum member; may be overridden

New in version 3.6: _missing_, _order_, _generate_next_value_

New in version 3.7: _ignore_

From https://github.com/python/cpython/blob/848037c1476ddf86dd2798fca35527a63c764a8a/Lib/enum.py#L653-L661

    @DynamicClassAttribute
    def name(self):
        """The name of the Enum member."""
        return self._name_

    @DynamicClassAttribute
    def value(self):
        """The value of the Enum member."""
        return self._value_

name and value both are wrapper of _name_ and _value.

From https://github.com/python/cpython/blob/848037c1476ddf86dd2798fca35527a63c764a8a/Lib/enum.py#L575-L581

        # still not found -- try _missing_ hook
        try:
            exc = None
            result = cls._missing_(value)
        except Exception as e:
            exc = e
            result = None

The type of value should to be consistent with __new__ parameter which is object. But the return type is not determinate. It seems like it can be Any.

From the doc example, _order_ should be str.

I'm not sure about _generate_next_value_. From https://github.com/python/cpython/blob/848037c1476ddf86dd2798fca35527a63c764a8a/Lib/enum.py#L380-L406

        if isinstance(names, (tuple, list)) and names and isinstance(names[0], str):
            original_names, names = names, []
            last_values = []
            for count, name in enumerate(original_names):
                value = first_enum._generate_next_value_(name, start, count, last_values[:])
                last_values.append(value)
                names.append((name, value))

It can infer that name is str, start is int, count is int and last_values could be List[Any]. But in the docstring of Flag(subclass of Enum).

        name: the name of the member
        start: the initital start value or None
        count: the number of existing members
        last_value: the last value assigned or None

start could be None. But I don't see anywhere passing None.

Another problem is _generate_next_value_ is not decorated by staticmethod, mypy will report Self argument missing for a non-static method (or an invalid type for self).

@srittau
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Thank you for the pull request. Aside from the comments below, a few style nits:

  • New annotations should use PEP 526-style variable annotations, i.e. _name_: str etc., even if the surrounding code doesn't use them yet. If you prefer you could also change existing fields to PEP 526-style.
  • We try to minimize vertical whitespace in stubs. Classes bodies should have no blank lines.
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Hanaasagi added some commits Mar 6, 2019

@srittau

srittau approved these changes Mar 6, 2019

@srittau srittau merged commit b588d43 into python:master Mar 6, 2019

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