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A lightweight library to perform deep merges of python dictionaries

Project description

DeepMerge

A lightweight python package for performing deep-merges of python dictionaries

Usage is simple:

from pydeepmerge import deep_merge

> some_data = {'foo': {'bar': 'baz', 'spam': 'eggs'}, 'ham': 'eggs'}
> more_data = {'spam': {'eggs': 'ham'}, 'foo': {'baz': 'bar', 'bar': 'foo'}}
> deep_merge(some_data, more_data)
{'foo': {'bar': 'foo', 'baz': 'bar', 'spam': 'eggs'}, 'spam': {'eggs': 'ham'}, 'ham': 'eggs'}

pydeepmerge also allows users to specify their own merge strategy function. By default, it uses the function prefer_right.

A merge strategy is any function that can accept exactly two inputs. The output of the merge strategy function should be what the merge result between two values should be.

When writing your own merge strategy function, keep in mind that if the key does not exist on the left-hand mapping, the value Key.NoKeyFound will be passed to the first parameter of the function. This is done deliberately so the user can determine if they want to do special behaviour if it is the first occurrence of the key in the sequence of dictionaries.

An example of a merge strategy function can be found below:

from pydeepmerge import deep_merge
from pydeepmerge.types import Key
from typing import Mapping

def pick_shallower(left_value, right_value):
    if left_value is Key.NoKeyFound:
        return right_value
    
    if isinstance(right_value, Mapping):
        if not isinstance(left_value, Mapping):
            return left_value
        return deep_merge(left_value, right_value)
    
    return right_value

The deep_merge function does not mutate any mapping but instead creates a new dictionary.

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