How to add a function to existing class/object in Python

Question

I am reading a JSON object using Python. Below is the example.

var name = jsonObj['f_name'];

I want to define a function which can be directly called from jsonObj. Below is the pseudo code.

def get_attribute(key):
  if key in this
    return this[key]
  else
    return ''

And then I want to use this function as shown below.

jsonObj.get_attribute('f_name')

Let me know if this is possible. Please guide me on achieving this.

You could write a class that can be construded from the JSON data. Otherwise, python deserializes it into a dict which is meant to be used as a Map, not an object with methods — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Mar 6, 2020 at 4:49

David542 · Accepted Answer · 2020-03-06 04:03:13Z

1

Arun answers this, but as a fallback you can also use a function or another value. For example:

import json    
jsonObj=json.loads('{"f_name": "peter"}')

jsonObj.get('f_name')
# u'peter'

jsonObj.get('x_name','default')
# 'default'

jsonObj.get('x_name',jsonObj.get('f_name')) # or could just place it after the 
                                            # `get` with an or
# u'peter'

answered Mar 6, 2020 at 4:03

David542

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4 Comments

Arun Augustine Over a year ago

well explained 👍🏻👍🏻

Neeraj Kumar Over a year ago

Yes.. This helped. Is there any flavour of get which can get nested attributes as well. Like record['address']['postal_code'] ?

David542 Over a year ago

@NeerajKumar Yes, you could do record.get('address', {}).get('postal_code')

Neeraj Kumar Over a year ago

@David542 Thanks for helping me out. Just out of curiosity, is Python capable of providing functionality to define a function and attach it to an existing class or object. Please refer to the code in my question.

Arun Augustine · Accepted Answer · 2020-03-06 03:56:15Z

1

I think you should use get

>>> dictionary = {"message": "Hello, World!"}
>>> dictionary.get("message", "")
'Hello, World!'
>>> dictionary.get("test", "")
''

answered Mar 6, 2020 at 3:56

Arun Augustine

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