Python deep merge dict

merge_dict.py

import pytest


def merge_dict(a, b):
    for key in b:
        if key in a:
            if isinstance(a[key], dict) and isinstance(b[key], dict):
                merge_dict(a[key], b[key])
            elif a[key] == b[key]:
                pass
            elif isinstance(a[key], list) and isinstance(b[key], list):
                a[key] += b[key]
            else:
                raise Exception('Conflict')
        else:
            a[key] = b[key]
    return a


def test_merge_dict():
    a = {'foo': 'boo'}
    b = {'bar': 'zoo'}
    expected_result = {
        'foo': 'boo',
        'bar': 'zoo'
    }
    result = merge_dict(a, b)
    assert result == expected_result


def test_merge_dict_deep():
    a = {
        'foo': {
            'bar': 'boo',
        }
    }
    b = {
        'foo': {
            'baz': 'zoo',
        }
    }
    expected_result = {
        'foo': {
            'bar': 'boo',
            'baz': 'zoo',
        }
    }
    result = merge_dict(a, b)
    assert result == expected_result


def test_merge_dict_list():
    a = {
        'foo': [
            'boo'
        ]
    }
    b = {
        'foo': [
            'baz'
        ]
    }
    expected_result = {
        'foo': [
            'boo',
            'baz',
        ]
    }
    result = merge_dict(a, b)
    assert result == expected_result


def test_merge_dict_conflict():
    a = {
        'foo': [
            'boo'
        ]
    }
    b = {
        'foo': {
            'baz': 'zoo',
        }
    }
    with pytest.raises(Exception):
        merge_dict(a, b)