How to create 'empty' object with desired field

Question

For test purposes I need to create something like an empty object with some particular fields. Let me clarify by example:

Currently there is a structure:

var = {
    'blas': {
        'bla':       0.250,
        'bla1':        0.300,
        'bla2': 6,
        ...
    },
    'somth1': self.smth1,
    'something': [
        { 'h1': 66.00 },
        { 'h2': 47.00 },
        { 'h3': 85.00 },
        { 'h4': 32.00 },
        { 'h5': 34.00 }
    ],
    'this_has_to_be_object'.field: 1
}

The thing I want is for 'this_has_to_be_object' to be an actual object to which I can add some fields and set values. The objective of such behaviour is to test another function that operates with 'this_has_to_be_object'.field.

Why not just create an empty dictionary or that value then? Or do you need something that supports arbitrary attributes instead of keys? — Martijn Pieters
– Martijn Pieters, Commented May 9, 2014 at 12:11
It seems ("For test purposes...") that he's constructing dummy data to send to some code for testing. — RemcoGerlich
– RemcoGerlich, Commented May 9, 2014 at 12:20

RemcoGerlich · Accepted Answer · 2014-05-09 12:16:56Z

1

Namedtuples are on way, if they don't have to be mutable:

from collections import namedtuple

MyTupleType = namedtuple('MyTupleType', ['field'])

yourobject = MyTupleType(field=3)

print(yourobject.field)  # prints 3

If it's for testing, then using the Mock library is also handy (see http://www.voidspace.org.uk/python/mock/ ; unittest.mock is part of the standard library since Python 3.3 as well).

yourobject = MagicMock()
yourobject.field = 3

Note that yourobject now has any field or method you try to access on it, and their values are all yet another MagicMock instance. It's a very powerful unit testing tool.

Lastly you can just create a boring dummy class:

class Dummy(object):
    pass

yourobject = Dummy()
yourobject.field = 3

answered May 9, 2014 at 12:16

RemcoGerlich

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1 Comment

Igor Over a year ago

Thank you very much! I've taken a MagickMock()-way as a solution to my problem.

Sahil kalra · Accepted Answer · 2014-05-09 12:26:02Z

1

Why not use a Default dict here.e.g.

var  = defaultdict(int)

var.update({
    'blas': {
        'bla':       0.250,
        'bla1':        0.300,
        'bla2': 6,
        ...
    },
    'somth1': self.smth1,
    'something': [
        { 'h1': 66.00 },
        { 'h2': 47.00 },
        { 'h3': 85.00 },
        { 'h4': 32.00 },
        { 'h5': 34.00 }
    ],
    'this_has_to_be_object'.field: 1
}
)

Now var['anything'] would always return with 0.

I guess that is the functionality you require for testing, Right ?

answered May 9, 2014 at 12:26

Sahil kalra

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1 Comment

Igor Over a year ago

It looks like so. I've chosen a MagickMock as the solution since it's more suitable here. Thank you!

taymedee · Accepted Answer · 2014-05-09 12:31:51Z

1

var = {
'blas': {
    'bla':       0.250,
    'bla1':        0.300,
    'bla2': 6,
    ...
},
'somth1': self.smth1,
'something': [
    { 'h1': 66.00 },
    { 'h2': 47.00 },
    { 'h3': 85.00 },
    { 'h4': 32.00 },
    { 'h5': 34.00 }
],
'this_has_to_be_object':{'field': '1'}

}

this is already a object, if you said you want to add some field inside you can do it like

...this_has_to_be_object.newField = 3;

isn't this what you want?

edited May 9, 2014 at 12:31

answered May 9, 2014 at 12:17

taymedee

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1 Comment

Igor Over a year ago

Yes, thank you - it's exactly what I wanted to know :)

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