My code errors out with the following code:

from .db import db, environment, SCHEMA, add_prefix_for_prod
from sqlalchemy import Index

class Capstone(db.Model):
    __tablename__ = "capstones"

    if environment == "production":
        __table_args__ = (
        {'schema': SCHEMA},
        Index('capstone_user_id_idx', 'user_id')
    )

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(50), nullable=False)
    url = db.Column(db.String(150))
    description = db.Column(db.String(1000), nullable=False)
    cloned_from = db.Column(db.String(75), nullable=False)
    user_id = db.Column(db.String(75), nullable=False)
    created_at = db.Column(db.TIMESTAMP)

    # relations
    capstone_images = db.relationship("CapstoneImage", back_populates="capstone")
    reviews = db.relationship("Review", back_populates="capstone")

    def to_dict(self):
        return {
           ...
        }

i get the error: sqlalchemy.exc.ArgumentError: 'SchemaItem' object, such as a 'Column' or a 'Constraint' expected, got {'schema': 'captracker'}

Because I only need indexing for user_id, I can add index=True to the user_id column and remove the Index() from the tuple __table_args__ = {'schema': SCHEMA}, this fixes the error. Why does this work and not the previous setup?