Dynamic enum with FastApi

Sometimes you need dynamic enumerations, such as some selector options from  database, but you will find that it seems like an the enumeration can only be modified at app startup. Try this:

	from random import randint
	from fastapi import FastAPI
	from enum import Enum
	app = FastAPI()
	class DynamicEnum(Enum):
	pass
	@app.get("/")
	async def root(e: DynamicEnum):
	return {"e": e}
	@app.get("/rand-enum")
	async def rand_enum():
	class EmptyEnum(Enum): pass
	global DynamicEnum
	new_enum = EmptyEnum(
	'DynamicEnum',
	{
	**{f'{k}-{randint(0, 10)}': f'value-{randint(0, 100)}' for k in range(5)}
	}
	)
	DynamicEnum._member_map_ = new_enum._member_map_
	DynamicEnum._member_names_ = new_enum._member_names_
	DynamicEnum._value2member_map_ = new_enum._value2member_map_
	# It doesn't work because fastapi always holds a reference to the original enum
	# DynamicEnum = new_enum
	return {"message": DynamicEnum._member_map_}
	if __name__ == "__main__":
	import uvicorn
	uvicorn.run("test-enum:app", host='0.0.0.0', debug=True, reload=True, workers=1)

view raw dynamic-enum.py hosted with ❤ by GitHub

myuan@jxtkfuwuqi ~> curl 10.242.155.222:8000
{"detail":[{"loc":["query","e"],"msg":"field required","type":"value_error.missing"}]}⏎
myuan@jxtkfuwuqi ~> curl 10.242.155.222:8000/rand-enum
{"message":{"0-7":"value-85","1-8":"value-6","2-5":"value-10","3-5":"value-99","4-4":"value-14"}}⏎       
myuan@jxtkfuwuqi ~> curl '10.242.155.222:8000?e=value-10'
{"e":"value-10"}⏎
myuan@jxtkfuwuqi ~> curl '10.242.155.222:8000?e=value-9'
{"detail":[{"loc":["query","e"],"msg":"value is not a valid enumeration member; permitted: 'value-85', 'value-6', 'value-10', 'value-99', 'value-14'","type":"type_error.enum","ctx":{"enum_values":["value-85","value-6","value-10","value-99","value-14"]}}]}⏎
myuan@jxtkfuwuqi ~> curl '10.242.155.222:8000?e=value-11'
{"detail":[{"loc":["query","e"],"msg":"value is not a valid enumeration member; permitted: 'value-85', 'value-6', 'value-10', 'value-99', 'value-14'","type":"type_error.enum","ctx":{"enum_values":["value-85","value-6","value-10","value-99","value-14"]}}]}⏎

Enumeration constraints are still in effect while the enumeration is modified