Is there an Object spread syntax in python 2.7x like in Javascript?

Question

How can I spread an objects/dict(?) properties and into a new object/dict?

Simple Javascript:

const obj = {x: '2', y: '1'}
const thing = {...obj, x: '1'}
// thing = {x: '1', y: 1}

Python:

regions = []
for doc in locations_addresses['documents']:
   regions.append(
        {
            **doc, # this will not work
            'lat': '1234',
            'lng': '1234',

        }
    )
return json.dumps({'regions': regions, 'offices': []})

how about [argument unpacking?](https://caisbalderas.com/blog/python-function-unpacking-args-and-kwargs/) — Felipe, Dec 18 '17 at 20:21

juanpa.arrivillaga · Accepted Answer · 2017-12-18T20:32:59.540

63

If you had Python >=3.5, you can use key-word expansion in dict literal:

>>> d = {'x': '2', 'y': '1'}
>>> {**d, 'x':1}
{'x': 1, 'y': '1'}

This is sometimes referred to as "splatting".

If you are on Python 2.7, well, there is no equivalent. That's the problem with using something that is over 7 years old. You'll have to do something like:

>>> d = {'x': '2', 'y': '1'}
>>> x = {'x':1}
>>> x.update(d)
>>> x
{'x': '2', 'y': '1'}

edited Dec 18 '17 at 20:32

answered Dec 18 '17 at 20:25

juanpa.arrivillaga

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This is a really nice approach. However, I'm getting a `SyntaxError` on Python 2.7.x – Matias Cicero Dec 18 '17 at 20:27
File "", line 366 **doc, ^ SyntaxError: invalid syntax I updated the question – Armeen Harwood Dec 18 '17 at 20:27
@MatthewHarwood yep, didn't realize you were on Python 2.7. You'r SOL if you want something like that which will work with dict-literals. – juanpa.arrivillaga Dec 18 '17 at 20:30
1

@MatiasCicero yes, just realized OP was on 2.7. This only works for Python >3 – juanpa.arrivillaga Dec 18 '17 at 20:31
Literally my first project in python and it's very legacy. maybe next time lol! thanks for the help – Armeen Harwood Dec 18 '17 at 20:32
@MatthewHarwood yea, especially with the release of 3.6, Python 3 is vastly superior to Python 2. python 3.7 looks like it's going to be even better. – juanpa.arrivillaga Dec 18 '17 at 20:33
@juanpa.arrivillaga Actually, there's something similar for older versions. Take a look at my answer. – Matias Cicero Dec 18 '17 at 20:35
@MatiasCicero yeah, that works, but you are limited by the acceptable order of arguments, i.e., positional arguments have to come before keyword-arguments. – juanpa.arrivillaga Dec 18 '17 at 20:39
Is `splatting` a python specific word or a generic one? In JavaScript there is `spread syntax`. – Mohammed Shareef C Aug 06 '19 at 11:05
1

@MohammedShareefC it's informal, but I don't think it's just Python. if you google "splat operator" you get hits for Ruby and PHP – juanpa.arrivillaga Aug 06 '19 at 18:11

score 6 · Answer 2 · edited Apr 18 '22 at 13:19

6

You can achieve this by creating a dict based on the original one, and then doing argument unpacking for the new/overridden keys:

regions.append(dict(doc, **{'lat': '1234', 'lng': '1234'}))

Note: Works in both python 2 and python 3

edited Apr 18 '22 at 13:19

Chandan

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answered Dec 18 '17 at 20:22

Matias Cicero

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Is there an Object spread syntax in python 2.7x like in Javascript?

2 Answers2

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