Must all Python instance variables be declared in def __init__?

Question

Or can they be declared otherwise?

The code below does not work:

class BinaryNode():
    self.parent = None
    self.left_child = None

Answer 1

Also, you can have class level variables, but I call them class constants.

class Connection(object):
    """helps you connect to the server at work"""
    YOUR_IP = '10.0.9.99'

    def __init__(self, username, password):
        self.ip = Connection.YOUR_IP
        self.un = username
        self.pw = password

    #...and so on