[sqlalchemy] What's the difference between the two syntax of declaring index?

[Bob Fang]

Hi I have seen two/three ways to declare index on table:

1. use index=True

class Model(Base):
    __tablename__ = "model"
    id = sa.Column(sa.Integer, primary_key=True)
    field_1 = sa.Column(sa.Integer, index=True)

2. use __table_args__:

class Model(Base):
    __tablename__ = "model"
    id = sa.Column(sa.Integer)
    field_1 = sa.Column(sa.Integer)

    __table_args__ = (sa.Index("field_1_index", "field_1"))

3. use Index statement:

class Model(Base):
    __tablename__ = "model"
    id = sa.Column(sa.Integer)
    field_1 = sa.Column(sa.Integer)

Index("field_1_index", "field1") 

My question is what's the difference between these 3? Also if I have mixed 
two of them, what will happen?  By this I mean consider the following 
example;

class Model(Base):
    __tablename__ = "model"
    id = sa.Column(sa.Integer, *primary_key=True*)
    field_1 = sa.Column(sa.Integer)

    __table_args__ = (*sa.Index("field_1_index", "field_1")*)

Here we are mixing method 1 and 2. From my experiment it seems Postgres can 
accept this without any problem but Sqlite rejects it outright. Why this 
happens?

Thanks!
Bob

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