CODEWITHSUNDEEP
pythonpython-3.7python-dataclasses
Nagabhushan S N
Nagabhushan S N

Reputation: 7267

Update dataclass fields from a dict in python

How can I update the fields of a dataclass using a dict?

Example:

@dataclass
class Sample:
    field1: str
    field2: str
    field3: str
    field4: str

sample = Sample('field1_value1', 'field2_value1', 'field3_value1', 'field4_value1')
updated_values = {'field1': 'field1_value2', 'field3': 'field3_value2'}

I want to do something like 

sample.update(updated_values)

Upvotes: 11

Views: 9134

Answers (3)

roschach
roschach

Reputation: 9336

@DanStewart's solution seems to work but when you see members that start and end with __ you should avoid modifying them directly: since python does not have private/protected visibility, __ is the way to warn the programmer that those methods/variables are only for within class usage, not intended to be part of the interface.

A better method is to use replace as in this answer

from dataclasses import replace
sample = replace(sample, **updated_values)

Upvotes: 2

Dan Stewart
Dan Stewart

Reputation: 121

Updating the underlying __dict__ seems to work if you have a basic dataclass:

sample.__dict__.update({ 'field1': 'value1' })

Upvotes: 10

bb1950328
bb1950328

Reputation: 1599

One way is to make a small class and inherit from it:

class Updateable(object):
    def update(self, new):
        for key, value in new.items():
            if hasattr(self, key):
                setattr(self, key, value)

@dataclass
class Sample(Updateable):
    field1: str
    field2: str
    field3: str
    field4: str

You can read this if you want to learn more about getattr and setattr

Upvotes: 10

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