[Python] Defining SQLAlchemy enum column with Python enum raises "ValueError: not a valid enum"

I am trying to follow this example to have an enum column in a table that uses Python's Enum type. I define the enum then pass it to the column as shown in the example, but I get ValueError: <enum 'FruitType'> is not a valid Enum. How do I correctly define a SQLAlchemy enum column with a Python enum?

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
import enum

app = Flask(__name__)
db = SQLAlchemy(app)

class FruitType(enum.Enum):
APPLE = "Crunchy apple"
BANANA = "Sweet banana"

class MyTable(db.Model):
id = db.Column(db.Integer, primary_key = True)
fruit_type = db.Column(enum.Enum(FruitType))


File "why.py", line 32, in <module>
class MyTable(db.Model):
File "why.py", line 34, in MyTable
fruit_type = db.Column(enum.Enum(FruitType))
File "/usr/lib/python2.7/dist-packages/enum/__init__.py", line 330, in __call__
return cls.__new__(cls, value)
File "/usr/lib/python2.7/dist-packages/enum/__init__.py", line 642, in __new__
raise ValueError("%s is not a valid %s" % (value, cls.__name__))
ValueError: <enum 'FruitType'> is not a valid Enum

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