Class factory to produce simple struct-like classes?

Question

While investigating Ruby I came across this to create a simple Struct-like class:

Person = Struct.new(:forname, :surname)
person1 = Person.new(\'John\', \'Do         


        

Answer 1

If you're running python <2.6 or would like to extend your class to do more stuff, I would suggest using the type() builtin. This has the advantage over your solution in that the setting up of __dict__ happens at class creation rather than instantiation. It also doesn't define an __init__ method and thus doesn't lead to strange behavior if the class calls __init__ again for some reason. For example:

def Struct(*args, **kwargs):
    name = kwargs.pop("name", "MyStruct")
    kwargs.update(dict((k, None) for k in args))
    return type(name, (object,), kwargs)

Used like so:

>>> MyStruct = Struct("forename", "lastname")

Equivalent to:

class MyStruct(object):
    forename = None
    lastname = None

While this:

>>> TestStruct = Struct("forename", age=18, name="TestStruct")

Is equivalent to:

class TestStruct(object):
    forename = None
    age = 18

Update

Additionally, you can edit this code to very easily prevent assignment of other variables than the ones specificed. Just change the Struct() factory to assign __slots__.

def Struct(*args, **kwargs):
    name = kwargs.pop("name", "MyStruct")
    kwargs.update(dict((k, None) for k in args))
    kwargs['__slots__'] = kwargs.keys()
    return type(name, (object,), kwargs)