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

As others have said, named tuples in Python 2.6/3.x. With older versions, I usually use the Stuff class:

class Stuff(object):
    def __init__(self, **kwargs):
        self.__dict__.update(kwargs)

john = Stuff(forename='John', surname='Doe')

This doesn't protect you from mispellings though. There's also a recipe for named tuples on ActiveState:

http://code.activestate.com/recipes/500261/

Answer 2

This is following up on Cide's answer (and probably only interesting for people who want to dig deeper).

I experienced a problem using Cide's updated definition of Struct(), the one using __slots__. The problem is that instances of returned classes have read-only attributes:

>>> MS = Struct('forename','lastname')
>>> m=MS()
>>> m.forename='Jack'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'MyStruct' object attribute 'forename' is read-only

Seems that __slots__ is blocking instance-level attributes when there are class attributes of same names. I've tried to overcome this by providing an __init__ method, so instance attributes can be set at object creation time:

def Struct1(*args, **kwargs):
    def init(self):
        for k,v in kwargs.items():
            setattr(self, k, v)
    name = kwargs.pop("name", "MyStruct")
    kwargs.update(dict((k, None) for k in args))
    return type(name, (object,), {'__init__': init, '__slots__': kwargs.keys()})

As a net effect the constructed class only sees the __init__ method and the __slots__ member, which is working as desired:

>>> MS1 = Struct1('forename','lastname')
>>> m=MS1()
>>> m.forename='Jack'
>>> m.forename
'Jack'

Answer 3

The Python package esu brings a struct that can provide almost the same functionality:

from esu import Struct

Customer = Struct(
        'Customer',
        'name', 'address',
        methods={
            'greeting': lambda self: "Hello {}".format(self.__dict__['name'])
        })

dave = Customer()
dave.name = 'Dave'
dave.greeting() # => Hello Dave

from https://torokmark.github.io/post/python-struct/

Answer 4

There is namedtuple

>>> from collections import namedtuple
>>> Person = namedtuple("Person", ("forename", "surname"))
>>> john = Person("John", "Doe")
>>> john.forename 
'John'
>>> john.surname 
'Doe'

Answer 5

An update of ThomasH's variant:

def Struct(*args, **kwargs):
    def init(self, *iargs, **ikwargs):
        for k,v in kwargs.items():
            setattr(self, k, v)
        for i in range(len(iargs)):
            setattr(self, args[i], iargs[i])
        for k,v in ikwargs.items():
            setattr(self, k, v)

    name = kwargs.pop("name", "MyStruct")
    kwargs.update(dict((k, None) for k in args))
    return type(name, (object,), {'__init__': init, '__slots__': kwargs.keys()})

This allows parameters (and named parameters) passed into __init__() (without any validation - seems crude):

>>> Person = Struct('fname', 'age')
>>> person1 = Person('Kevin', 25)
>>> person2 = Person(age=42, fname='Terry')
>>> person1.age += 10
>>> person2.age -= 10
>>> person1.fname, person1.age, person2.fname, person2.age
('Kevin', 35, 'Terry', 32)
>>> 

Update

Having a look into how namedtuple() does this in collections.py. The class is created and expanded as a string and evaluated. Also has support for pickling and so on, etc.

Answer 6

If you're using Python 2.6, try the standard library namedtuple class.

>>> from collections import namedtuple
>>> Person = namedtuple('Person', ('forename', 'surname'))
>>> person1 = Person('John', 'Doe')
>>> person2 = Person(forename='Adam', surname='Monroe')
>>> person1.forename
'John'
>>> person2.surname
'Monroe'

Edit: As per comments, there is a backport for earlier versions of Python