Meaning of < > in Python

Question

What type of Python data structure is represented by "< >", like this.

[<Board 1>, <Board 2>, <Board 3>]

I came across this while working with the Flask-SQLAlchemy library for Python3. See code below.

class Board(db.Model):

  __tablename__ = 'boards'

  id = db.Column(db.Integer, primary_key=True)
  name = db.Column(db.String(256), unique=True, nullable=False)
  description = db.Column(db.String(256))

  def __init__(id, name, description):
    self.id = id
    self.name = name
    self.description = description


tuple_boards = Board.query.all()

print (tuple_boards)
[<Board 1>, <Board 2>, <Board 3>]

Answer 1

It's not a data structure. This is just how Flask-SQLAlchemy represents an instance of your model as a string with Model.__repr__:

class Model(object):
    ...

    def __repr__(self):
        identity = inspect(self).identity
        if identity is None:
            pk = "(transient {0})".format(id(self))
        else:
            pk = ', '.join(to_str(value) for value in identity)
        return '<{0} {1}>'.format(type(self).__name__, pk)

It's a whole lot more useful than the default object.__repr__:

In [1]: class Thing(object):
  ...       pass
  ...

In [2]: [Thing(), Thing(), Thing()]
Out[2]:
[<__main__.Thing at 0x10c8826a0>,
 <__main__.Thing at 0x10c8820b8>,
 <__main__.Thing at 0x10c8822e8>]

You can put whatever you want in __repr__, but it's usually best to unambiguously represent your object as a string:

In [4]: class OtherThing(object):
  ...       def __repr__(self):
  ...           return "I'm an arbitrary string"
  ...

In [5]: [OtherThing(), OtherThing()]
Out[5]: [I'm an arbitrary string, I'm an arbitrary string]

I've often seen the <...> string used for object representations that aren't valid Python code, as many other built-in objects' __repr__esentations are valid Python code that reconstructs an equivalent object.