Python create a dictionary using new and add an attribute for each key

Question

I am building a python class in which I create a dictionnary using the method "new". Then, I would like to define a method to affect a unit for some of the keys. Below an example of the code:

class MyClass(object):
  def __new__(cls):
    dict = {key1:None, key2:None}
    return dict

  def unit(self, unit):
    self[KEY].unit = unit

Where, in the unit method, KEY should take any key of the dictionnary. Could you please help me to understand how to code it?

In advance thank you,

Do not use the __new__ method. It's almost always a mistake and is definitely so in your example. You should be subclassing dict. It is also not clear where or how the magic KEY var is defined. I recommend you rephrase your question in terms of your goals rather than in terms of getting your example to work using the __new__() method. — Kurtis Rader
– Kurtis Rader, Commented May 3, 2018 at 3:09

Dschoni · Accepted Answer · 2018-05-02 13:36:01Z

1

I'm not sure, why you want to use __new__ instead of __init__, but you can simply iterate through all keys in the dictionary by doing:

class dictionary_setter:
  some_dic = {'key1':1, 'some_other_key':2, 'just another key':3}

def __init__(self,keys):
  self.some_dic = {}
  for k in keys:
    self.some_dic[k]='some_value'

a_test_dic = dictionary_setter(['key1','key2'])
print(a_test_dic.some_dick['key1'])

Turning a string into a variable is another topic, but you can simply refer to the dictionary entry via dot syntax.

edited May 2, 2018 at 13:36

answered May 2, 2018 at 13:21

Dschoni

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5 Comments

linksse Over a year ago

I can not return a dictionary with init. And I would like to do something like: ` from MyClass import * dict = MyClass() dict["key1"].unit = "m/s" `

Dschoni Over a year ago

You don't have to. You can simply refer to the dictionary. Are you coming from C/Java over to python?

linksse Over a year ago

From fortran to python

Dschoni Over a year ago

I updated the example to show, how you can append a dictionary to the instance of a class.

linksse Over a year ago

I agree with that, but I still cannot affect an attirbute UNIT to "some_dic" using only the key. Cf. def unit(self, unit): self.some_dic[key].unit = unit

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