flask-route-enum-converter.py

from enum import Enum, EnumMeta

from flask import Flask, current_app
from werkzeug.routing import BaseConverter, ValidationError


def setup_enum_converter(enum_to_convert):

    if not isinstance(enum_to_convert, (Enum, EnumMeta,)):
        raise ValueError(f'{enum_to_convert.__name__} is not an Enum')

    class ConfiguredEnumConverter(BaseConverter):
        def to_python(self, value):
            try:
                return enum_to_convert[value]
            except (KeyError, IndexError, ValueError) as exc:
                current_app.logger.exception(exc)
                raise ValidationError from exc

        def to_url(self, obj):
            if not isinstance(obj, enum_to_convert):
                raise ValidationError()

            return obj.name

    return ConfiguredEnumConverter
  

# Can be a static Enum or a dynamic one:

DynamicEnum = Enum('DynamicEnum', {'ONE': 1, 'TWO': 2, 'THREE': 3})

class StaticEnum(Enum):
    FOUR = 4
    FIVE = 5
    SIX = 6
  
  
app = Flask(__name__)
  
# Add the Enum converter to the app's available converters before the route/blueprint that needs it
# `MyDynamicEnum`/`MyStaticEnum` corresponds to the name that we use in the route
app.url_map.converters.update(
    MyDynamicEnum=setup_enum_converter(DynamicEnum),
    MyStaticEnum=setup_enum_converter(StaticEnum),
)


@app.route('/dynamic/<MyDynamicEnum:param>')
def dynamic_enum(param):
    return f'{type(param)}->{param} = {param.value}'

@app.route('/static/<MyStaticEnum:param>')
def static_enum(param):
    return f'{type(param)}->{param} = {param.value}'


# On running this mini Flask app, you get:
#
# $ curl http://localhost:5000/static/FIVE
# <enum 'StaticEnum'>->StaticEnum.FIVE: FIVE = 4
#
# $ curl http://localhost:5000/dynamic/ONE
# <enum 'DynamicEnum'>->DynamicEnum.ONE = 1
#