How do I put docstrings on Enums? - python-2.7

Question

Python 3.4 has a new enum module and Enum data type. If you are unable to switch to 3.4 yet, Enum has been backported.
Since Enum members support docstrings, as pretty much all python objects do, I would like to set them. Is there an easy way to do that?

Answer 1

Yes there is, and it's my favorite recipe so far. As a bonus, one does not have to specify the integer value either. Here's an example:
class AddressSegment(AutoEnum):
misc = "not currently tracked"
ordinal = "N S E W NE NW SE SW"
secondary = "apt bldg floor etc"
street = "st ave blvd etc"
You might ask why I don't just have "N S E W NE NW SE SW" be the value of ordinal? Because when I get its repr seeing <AddressSegment.ordinal: 'N S E W NE NW SE SW'> gets a bit clunky, but having that information readily available in the docstring is a good compromise.
Here's the recipe for the Enum:
class AutoEnum(enum.Enum):
"""
Automatically numbers enum members starting from 1.
Includes support for a custom docstring per member.
"""
#
def __new__(cls, *args):
"""Ignores arguments (will be handled in __init__."""
value = len(cls) + 1
obj = object.__new__(cls)
obj._value_ = value
return obj
#
def __init__(self, *args):
"""Can handle 0 or 1 argument; more requires a custom __init__.
0 = auto-number w/o docstring
1 = auto-number w/ docstring
2+ = needs custom __init__
"""
if len(args) == 1 and isinstance(args[0], (str, unicode)):
self.__doc__ = args[0]
elif args:
raise TypeError('%s not dealt with -- need custom __init__' % (args,))
And in use:
>>> list(AddressSegment)
[<AddressSegment.ordinal: 1>, <AddressSegment.secondary: 2>, <AddressSegment.misc: 3>, <AddressSegment.street: 4>]
>>> AddressSegment.secondary
<AddressSegment.secondary: 2>
>>> AddressSegment.secondary.__doc__
'apt bldg floor etc'
The reason I handle the arguments in __init__ instead of in __new__ is to make subclassing AutoEnum easier should I want to extend it further.

Answer 2

Anyone arriving here as a google search:
For many IDE's now in 2022, the following will populate intellisense:
class MyEnum(Enum):
"""
MyEnum purpose and general doc string
"""
VALUE = "Value"
"""
This is the Value selection. Use this for Values
"""
BUILD = "Build"
"""
This is the Build selection. Use this for Buildings
"""
Example in VSCode:

Answer 3

This does not directly answer the question, but I wanted to add a more robust version of #Ethan Furman's AutoEnum class which uses the auto enum function.
The implementation below works with Pydantic and does fuzzy-matching of values to the corresponding enum type.
Usage:
In [2]: class Weekday(AutoEnum): ## Assume AutoEnum class has been defined.
...: Monday = auto()
...: Tuesday = auto()
...: Wednesday = auto()
...: Thursday = auto()
...: Friday = auto()
...: Saturday = auto()
...: Sunday = auto()
...:
In [3]: Weekday('MONDAY') ## Fuzzy matching: case-insensitive
Out[3]: Monday
In [4]: Weekday(' MO NDAY') ## Fuzzy matching: ignores extra spaces
Out[4]: Monday
In [5]: Weekday('_M_onDa y') ## Fuzzy matching: ignores underscores
Out[5]: Monday
In [6]: %timeit Weekday('_M_onDay') ## Fuzzy matching takes ~1 microsecond.
1.15 µs ± 10.9 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)
In [7]: %timeit Weekday.from_str('_M_onDay') ## You can further speedup matching using from_str (this is because _missing_ is not called)
736 ns ± 8.89 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)
In [8]: list(Weekday) ## Get all the enums
Out[8]: [Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday]
In [9]: Weekday.Monday.matches('Tuesday') ## Check if a string matches a particular enum value
Out[9]: False
In [10]: Weekday.matches_any('__TUESDAY__') ## Check if a string matches any enum
Out[10]: True
In [11]: Weekday.Tuesday is Weekday(' Tuesday') and Weekday.Tuesday == Weekday('_Tuesday_') ## `is` and `==` work as expected
Out[11]: True
In [12]: Weekday.Tuesday == 'Tuesday' ## Strings don't match enum values, because strings aren't enums!
Out[12]: False
In [13]: Weekday.convert_keys({ ## Convert matching dict keys to an enum. Similar: .convert_list, .convert_set
'monday': 'alice',
'tuesday': 'bob',
'not_wednesday': 'charles',
'THURSDAY ': 'denise',
})
Out[13]:
{Monday: 'alice',
Tuesday: 'bob',
'not_wednesday': 'charles',
Thursday: 'denise'}
The code for AutoEnum can be found below.
If you want to change the fuzzy-matching logic, then override the classmethod _normalize (e.g. returning the input unchanged in _normalize, will perform exact matching).
from typing import *
from enum import Enum, auto
class AutoEnum(str, Enum):
"""
Utility class which can be subclassed to create enums using auto().
Also provides utility methods for common enum operations.
"""
#classmethod
def _missing_(cls, enum_value: Any):
## Ref: https://stackoverflow.com/a/60174274/4900327
## This is needed to allow Pydantic to perform case-insensitive conversion to AutoEnum.
return cls.from_str(enum_value=enum_value, raise_error=True)
def _generate_next_value_(name, start, count, last_values):
return name
#property
def str(self) -> str:
return self.__str__()
def __repr__(self):
return self.__str__()
def __str__(self):
return self.name
def __hash__(self):
return hash(self.__class__.__name__ + '.' + self.name)
def __eq__(self, other):
return self is other
def __ne__(self, other):
return self is not other
def matches(self, enum_value: str) -> bool:
return self is self.from_str(enum_value, raise_error=False)
#classmethod
def matches_any(cls, enum_value: str) -> bool:
return cls.from_str(enum_value, raise_error=False) is not None
#classmethod
def does_not_match_any(cls, enum_value: str) -> bool:
return not cls.matches_any(enum_value)
#classmethod
def _initialize_lookup(cls):
if '_value2member_map_normalized_' not in cls.__dict__: ## Caching values for fast retrieval.
cls._value2member_map_normalized_ = {}
for e in list(cls):
normalized_e_name: str = cls._normalize(e.value)
if normalized_e_name in cls._value2member_map_normalized_:
raise ValueError(
f'Cannot register enum "{e.value}"; '
f'another enum with the same normalized name "{normalized_e_name}" already exists.'
)
cls._value2member_map_normalized_[normalized_e_name] = e
#classmethod
def from_str(cls, enum_value: str, raise_error: bool = True) -> Optional:
"""
Performs a case-insensitive lookup of the enum value string among the members of the current AutoEnum subclass.
:param enum_value: enum value string
:param raise_error: whether to raise an error if the string is not found in the enum
:return: an enum value which matches the string
:raises: ValueError if raise_error is True and no enum value matches the string
"""
if isinstance(enum_value, cls):
return enum_value
if enum_value is None and raise_error is False:
return None
if not isinstance(enum_value, str) and raise_error is True:
raise ValueError(f'Input should be a string; found type {type(enum_value)}')
cls._initialize_lookup()
enum_obj: Optional[AutoEnum] = cls._value2member_map_normalized_.get(cls._normalize(enum_value))
if enum_obj is None and raise_error is True:
raise ValueError(f'Could not find enum with value {enum_value}; available values are: {list(cls)}.')
return enum_obj
#classmethod
def _normalize(cls, x: str) -> str:
## Found to be faster than .translate() and re.sub() on Python 3.10.6
return str(x).replace(' ', '').replace('-', '').replace('_', '').lower()
#classmethod
def convert_keys(cls, d: Dict) -> Dict:
"""
Converts string dict keys to the matching members of the current AutoEnum subclass.
Leaves non-string keys untouched.
:param d: dict to transform
:return: dict with matching string keys transformed to enum values
"""
out_dict = {}
for k, v in d.items():
if isinstance(k, str) and cls.from_str(k, raise_error=False) is not None:
out_dict[cls.from_str(k, raise_error=False)] = v
else:
out_dict[k] = v
return out_dict
#classmethod
def convert_keys_to_str(cls, d: Dict) -> Dict:
"""
Converts dict keys of the current AutoEnum subclass to the matching string key.
Leaves other keys untouched.
:param d: dict to transform
:return: dict with matching keys of the current AutoEnum transformed to strings.
"""
out_dict = {}
for k, v in d.items():
if isinstance(k, cls):
out_dict[str(k)] = v
else:
out_dict[k] = v
return out_dict
#classmethod
def convert_values(
cls,
d: Union[Dict, Set, List, Tuple],
raise_error: bool = False
) -> Union[Dict, Set, List, Tuple]:
"""
Converts string values to the matching members of the current AutoEnum subclass.
Leaves non-string values untouched.
:param d: dict, set, list or tuple to transform.
:param raise_error: raise an error if unsupported type.
:return: data structure with matching string values transformed to enum values.
"""
if isinstance(d, dict):
return cls.convert_dict_values(d)
if isinstance(d, list):
return cls.convert_list(d)
if isinstance(d, tuple):
return tuple(cls.convert_list(d))
if isinstance(d, set):
return cls.convert_set(d)
if raise_error:
raise ValueError(f'Unrecognized data structure of type {type(d)}')
return d
#classmethod
def convert_dict_values(cls, d: Dict) -> Dict:
"""
Converts string dict values to the matching members of the current AutoEnum subclass.
Leaves non-string values untouched.
:param d: dict to transform
:return: dict with matching string values transformed to enum values
"""
out_dict = {}
for k, v in d.items():
if isinstance(v, str) and cls.from_str(v, raise_error=False) is not None:
out_dict[k] = cls.from_str(v, raise_error=False)
else:
out_dict[k] = v
return out_dict
#classmethod
def convert_list(cls, l: List) -> List:
"""
Converts string list itmes to the matching members of the current AutoEnum subclass.
Leaves non-string items untouched.
:param l: list to transform
:return: list with matching string items transformed to enum values
"""
out_list = []
for item in l:
if isinstance(item, str) and cls.matches_any(item):
out_list.append(cls.from_str(item))
else:
out_list.append(item)
return out_list
#classmethod
def convert_set(cls, s: Set) -> Set:
"""
Converts string list itmes to the matching members of the current AutoEnum subclass.
Leaves non-string items untouched.
:param s: set to transform
:return: set with matching string items transformed to enum values
"""
out_set = set()
for item in s:
if isinstance(item, str) and cls.matches_any(item):
out_set.add(cls.from_str(item))
else:
out_set.add(item)
return out_set
#classmethod
def convert_values_to_str(cls, d: Dict) -> Dict:
"""
Converts dict values of the current AutoEnum subclass to the matching string value.
Leaves other values untouched.
:param d: dict to transform
:return: dict with matching values of the current AutoEnum transformed to strings.
"""
out_dict = {}
for k, v in d.items():
if isinstance(v, cls):
out_dict[k] = str(v)
else:
out_dict[k] = v
return out_dict

Answer 4

Functions and classes have docstrings, but most objects don't and do not even need them at all. There is no native docstring syntax for instance attributes, as they can be described exhaustively in the classes' docstring, which is also what I recommend you to do. Instances of classes normally also don't have their own docstrings, and enum members are nothing more than that.
Sure enough you could add a docstring to almost anything. Actually you can, indeed, add anything to almost anything, as this is the way python was designed. But it is neither useful nor clean, and even what #Ethan Furman posted seems like way to much overhead just for adding a docstring to a static property.
Long story short, even though you might not like it at first:
Just don't do it and go with your enum's docstring. It is more than enough to explain the meaning of its members.