Python create list of objects from list of 2 elements lists

Question

I have a list of lists of 2-element lists, e.g.:

[[[a, b], [c, d], [e, f]], [[g, h], [i, j], [k, l]]] 

and I want to create a list of objects with attributes from the two-element lists, like this:

[(obj.a = b, obj.c=d, obj.e=f), (obj.g=h, obj.i=j, obj.k=l)]

I tried many ways, but seems I really don't know how, creating an object like a = object() and setting attrs via object.__setattr__ didn't work for me.

Answer 1

You can't set arbitrary attributes on object instances:

>>> a = object()
>>> a.b = 'c'

Traceback (most recent call last):
  File "<pyshell#56>", line 1, in <module>
    a.b = 'c'
AttributeError: 'object' object has no attribute 'b'

Howver, you can create a Generic class that will allow you to:

class Generic(object):
    pass

Then, assuming your list contains string pairs:

l = [[['a', 'b'], ['c', 'd'], ['e', 'f']], 
     [['g', 'h'], ['i', 'j'], ['k', 'l']]]

you can iterate over it as follows:

out = []
for ll in l:
    obj = Generic()
    for attr, val in ll:
        setattr(obj, attr, val)
    out.append(obj)

---

Alternatively, you can use the three-argument form of type to create arbitrary classes, then create instances of those:

out = [type("Generic", (object,), dict(ll))() for ll in l]

Note that e.g.

>>> dict(l[0])
{'a': 'b', 'c': 'd', 'e': 'f'}

---

Finally, if you have an actual (not generic) object that takes e.g. a, c, e as arguments to __init__:

class Actual(object):
    def __init__(self, a, c, e):
        self.a = a
        self.c = c
        self.e = e

You can use dictionary unpacking to create an instance from the sub-list e.g. l[0]:

obj = Actual(**dict(l[0]))