Creating class instance from dictionary?

Question

I am trying to create class instance from dictionary that has keys more than class has attributes. I already read answers on the same question from this link: Creating class instance properties from a dictionary?. The problem is that I can't write __init__ in class definition as I want, because I'm using SQLAlchemy declarative style class definition. Also type('className', (object,), dict) creates wrong attributes that are not needed. Here is the solution that I found:

dict = {'key1': 'value1', 'key2': 'value2'}
object = MyClass(**dict)

But it does not work if dict has redundant keys:

dict = {'key1': 'value1', 'key2': 'value2', 'redundant_key': 'redundant_value'}
object = MyClass(**dict) # here need to ignore redundant_key

Are there any solutions except direct deleting all redundant keys from dict?

How do you want to write `__init__` for `MyClass`? Sorry I'm not familiar with SQLAlchemy declarative style class definitions. — Paul Rooney, May 08 '15 at 00:17
@RafaelCardoso redundant_key is a key that exists in a dictionary, but doesn't exist in class attributes. — Demyanov, May 08 '15 at 00:17
@PaulRooney `__init__` for MyClass such as in this answer http://stackoverflow.com/a/1639197/3700561 — Demyanov, May 08 '15 at 00:21
@RafaelCardoso Yes, I exactly know all class' attributes and dict keys and I can directly remove all "wrong keys" from dict and then use the solution that is mention above. But I don't think this is a right way — Demyanov, May 08 '15 at 00:26

score 14 · Accepted Answer · answered May 08 '15 at 00:46

Use a classmethod to filter the dict and return the object.

You then dont have to force your __init__ method to accept a dict.

import itertools

class MyClass(object):
    @classmethod
    def fromdict(cls, d):
        allowed = ('key1', 'key2')
        df = {k : v for k, v in d.iteritems() if k in allowed}
        return cls(**df)

    def __init__(self, key1, key2):
        self.key1 = key1
        self.key2 = key2

dict = {'key1': 'value1', 'key2': 'value2', 'redundant_key': 'redundant_value'}

ob = MyClass.fromdict(dict)

print ob.key1
print ob.key2

score 1 · Answer 2 · edited May 23 '17 at 12:14

1

The other solution is to Filter dict to contain only certain keys:

dict_you_want = { your_key: dict[your_key] for your_key in your_keys }

edited May 23 '17 at 12:14

Community

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answered May 08 '15 at 00:27

Brent Washburne

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And then add a line in your __init__function like:`self.__dict__.update(dict_you_want)` – Paul Cornelius May 08 '15 at 00:29

score 1 · Answer 3 · answered Aug 20 '19 at 12:43

One of the special python magic methods of an object is object.__dict__ "A dictionary or other mapping object used to store an object’s (writable) attributes." So, by elevating this feature...

class MyClass(object):
   def __init__(self, **entries):
      self.__dict__.update(entries))

dict = {'key1': 'value1', 'key2': 'value2', 'redundant_key': 'redundant_value'}

ob = MyClass(**dict)

Note: It doesn't handle nested dictionary...

Creating class instance from dictionary?

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