How to create objects on the fly in python?

Question

How do I create objects on the fly in Python? I often want to pass information to my Django templates which is formatted like this:

{'test': [a1, a2, b2], 'test2': 'something else', 'test3': 1}

which makes the template look untidy. so I think it's better to just create an object which is like:

class testclass():
    self.test = [a1,a2,b2]
    self.test2 = 'someting else'
    self.test3 = 1
testobj = testclass()

so I can do:

{{ testobj.test }}
{{ testobj.test2 }}
{{ testobj.test3 }}

instead of calling the dictionary.

Since I just need that object once, is it possible to create it without writing a class first? Is there any short-hand code? Is it ok to do it like that or is it bad Python?

number5 · Answer 1 · 2011-12-21T02:29:38.793

34

You can use built-in type function:

testobj = type('testclass', (object,), 
                 {'test':[a1,a2,b2], 'test2':'something else', 'test3':1})()

But in this specific case (data object for Django templates), you should use @Xion's solution.

edited Dec 21 '11 at 02:29

answered Dec 20 '11 at 13:15

number5

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8

Please don't do this. Simple is better than complex. – Karl Knechtel Dec 20 '11 at 13:33
3

@number5 I will vote for your answer if you also suggest not to use this code! (at least not for this specific case) – Tommaso Barbugli Dec 20 '11 at 14:11
1

Although this is really handy for creating ad hoc objects for stubbing during testing, i.e. from a dictionary. Thanks. – Rohan Nicholls Dec 10 '14 at 13:54

score 29 · Answer 2 · answered Oct 26 '16 at 11:53

29

There is another solution in Python 3.3+ types.SimpleNamespace

from types import SimpleNamespace
test_obj = SimpleNamespace(a=1, b=lambda: {'hello': 42})

test_obj.a
test_obj.b()

answered Oct 26 '16 at 11:53

t_io

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score 27 · Accepted Answer · answered Dec 20 '11 at 13:19

27

In Django templates, the dot notation (testobj.test) can resolve to the Python's [] operator. This means that all you need is an ordinary dict:

testobj = {'test':[a1,a2,b2], 'test2':'something else', 'test3':1}

Pass it as testobj variable to your template and you can freely use {{ testobj.test }} and similar expressions inside your template. They will be translated to testobj['test']. No dedicated class is needed here.

answered Dec 20 '11 at 13:19

Xion

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thank you, that solved the django related part of my problem :) i just checked the other answer because people coming here from google would probably prefer to see the python related answer. – JasonTS Dec 20 '11 at 13:34
1

@JasonTS, the python related answer would be to use Karl Knechtel's answer of `collections.namedtuple`. – Duncan Dec 20 '11 at 13:47

score 17 · Answer 4 · answered Dec 20 '11 at 13:18

17

Use collections.namedtuple.

answered Dec 20 '11 at 13:18

Karl Knechtel

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Allows inheritance? – Memmo Jul 14 '23 at 08:27

score 3 · Answer 5 · edited Jul 28 '20 at 11:09

3

use building function type: document

>>> class X:
...     a = 1
...
>>> X = type('X', (object,), dict(a=1))

first and second X are identical

edited Jul 28 '20 at 11:09

confiq

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answered Dec 17 '17 at 11:55

Евгений Па

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Bob Stein · Answer 6 · 2020-11-04T22:38:07.867

2

Here's a rogue, minimalist way to create an object. A class is an object, so just commandeer the class definition syntax as if it were a Python object literal:

class testobj(object):
    test = [a1,a2,b2]
    test2 = 'something else'
    test3 = 1

Class variables are the members of the object, and are easily referenced:

assert testobj.test3 == 1

This is weird, a class never used as a class: it's never instantiated. But it's a low-clutter way to make an ad hoc, singleton object: The class itself is your object.

edited Nov 04 '20 at 22:38

answered Jul 22 '19 at 01:33

Bob Stein

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Note thant the class as an object have large memory footprint and sensible amount of time for it's creation. – intellimath Jun 22 '21 at 09:30
@intellimath your point that a class comes with a lot of baggage is a good one, and one should be aware of its consequences. I would note that computer memory gets cheaper while **human memory trends ever more precious**. A singleton object that's not used repetitively has little cost. A lean syntax that's quick to read and understand has solid benefits. – Bob Stein Jun 22 '21 at 12:01

score 1 · Answer 7 · answered Sep 21 '20 at 13:37

1

for the sake of completeness, there is also recordclass:

from recordclass import recordclass
Test = recordclass('Test', ['test', 'test1', 'test2'])
foo = Test(test=['a1','a2','b2'], test1='someting else', test2=1)

print(foo.test)
.. ['a1', 'a2', 'b2']

answered Sep 21 '20 at 13:37

Daniel Schneider

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score 1 · Answer 8 · answered Aug 09 '21 at 18:38

if you just need a "QuickRecord" you can simply declare a empty class
and you can use it without having to instantiate an object...
(just seize the dynamic features of python language... "á la Javascript")

# create an empty class...
class c1:pass

# then just add/change fields at your will
c1.a = "a-field"
c1.b = 1
c1.b += 10
print( c1.a, " -> ", c1.b )

# this has even the 'benesse' of easealy taking a 
# snapshot whenever you want

c2 = c1()
print( c2.a, " -> ", c2.b )

Vader · Answer 9 · 2011-12-20T13:38:06.500

0

The code below also require a class to be created however it is shorter:

 >>>d = {'test':['a1','a2','b2'], 'test2':'something else', 'test3':1}
 >>> class Test(object):
 ...  def __init__(self):
 ...   self.__dict__.update(d)
 >>> a = Test()
 >>> a.test
 ['a1', 'a2', 'b2']
 >>> a.test2
 'something else'

edited Dec 20 '11 at 13:38

answered Dec 20 '11 at 13:28

Vader

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How to create objects on the fly in python?

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