How do I write a one-liner for the following?

class MyClass(): content = {}
obj = MyClass()

You can use type as an alternative way to create a class:

MyClass = type('MyClass', (object,), {'content':{}})
obj = MyClass()

or, in one line without binding the class to a name:

obj = type('MyClass', (object,), {'content':{}})()

The first argument being the name, the second the bases and the third the class namespace.