Converting a configuration dictionary to a Python object with optional keys

user_17191838 0
Viewed 94

Let's say i have a class:

class Foo():
    """A class with attr1 and attr2."""
    def __init__(self, attr_1: str = "", attr_2: int = 0):
        self.attr_1 = attr_1
        self.attr_2 = attr_2

And a configuration dict:

{
    "attr_1": "qack",
    "attr_2": 10
}

Note that sometimes, the configuration dict may have different key names, but internally, the program has a way to map a key's value in the dict to the corresponding attribute in the Foo attribute.

{
    "attr_1_diff_key_name": "qack",
    "2_attr": 10
}

I want to be able to write two functions that map the config dict to Foo and vice versa (aka, being able to convert the config dict into a Foo object and vice versa), like so:

def dict_to_foo(dict_config: dict):
    """Returns the Foo equivalent of the dictionary."""
    return Foo(
        attr_1 = dict_config["attr_1"],
        attr_2 = dict_config["attr_2"]
    )


def foo_to_dict(foo: Foo):
    """Returns the dictionary equivalent of the Foo object."""
    return {
        "attr_1": foo.attr_1,
        "attr_2": foo.attr_2
    }

it's pretty simple enough, but only when the config dict requires all attributes to be included.

In my project, that can't be the case. the config dict may omit a few attributes, where it's given that the program will use default values to replace the missing attributes.

config_dict_examples = [
    # Usual, has all attributes
    {
        "attr_1": "qack",
        "attr_2": 10
    },

    # "attr_2" omitted, it's understood here that the Foo equivalent will have attr_2 set to its default value from the __init__ function, in this case, 0.
    {
        "attr_1": "qack"
    },

    # In this case, all attributes are omitted, and thus the Foo equivalent will have both attr_1 and attr_2 set to its default value from the __init__ function, in this case, "" and 0 respectively.
    {}
]

My attempts to this problem is as follows:

def dict_to_foo_attempt_1(dict_config: dict):
    """Attempt 1 of dict_to_foo."""
    foo = Foo()

    if "attr_1" in dict_config:
        foo.attr_1 = dict_config["attr_1"]
    if "attr_2" in dict_config:
        foo.attr_2 = dict_config["attr_2"]

def foo_to_dict_attempt_1(foo: Foo):
    """Attempt 1 of foo_to_dict."""
    dict_config = {}
    default_foo = Foo()

    if foo.attr_1 != default_foo.attr_1:
        dict_config["attr_1"] = foo.attr_1
    if foo.attr_2 != default_foo.attr_2:
        dict_config["attr_2"] = foo.attr_2

Sure, this may be fine, but the general repetition, both from the conditional expression and the setting of the keys / variables in both functions, isn't something i really want.

Is there a way to make these functions cleaner? (say, without the repetitive parts?)

A common problem with solutions that require stuff like using **kwargs or vars() is that it's a bit too hacky and isn't supported by vscode's renaming feature, which makes refactoring hard in the future. This isn't what i want, but if there is no other way, i can still make do with it.

object dictionary python
4 Answers

The cleanest treatment way:

def dict_to_foo(dict_config: dict):
    """Returns the Foo equivalent of the dictionary."""
    return Foo(**dict_config)


def foo_to_dict(foo: Foo):
    """Returns the dictionary equivalent of the Foo object."""
    return vars(foo).copy()
user_179809310

Given you have a config dictionary with the real attributes names (you mentioned there's a mapping), you can iterate the dictionary and use setattr to set only the necessary attributes.

class Foo():
    """A class with attr1 and attr2."""
    def __init__(self, attr_1: str = "default_value", attr_2: int = 0):
        self.attr_1 = attr_1
        self.attr_2 = attr_2

config = {
    "attr_1": "qack",
    # "attr_2": 10
}

foo_obj = Foo()
print('Before using config: ',foo_obj.attr_1, foo_obj.attr_2)
for key, value in config.items():
    setattr(foo_obj, key, value)
print('After config: ',foo_obj.attr_1, foo_obj.attr_2)

The output:

Before using config:  default_value 0
After config:  qack 0
user_160039190

You could use dictionaries to map parameter names to dict keys and vice-versa:

FOO_ATTR_TO_KEY = {
    'attr_1': 'attr_1_diff_key_name',
}
FOO_KEY_TO_PARAM = {v: k for k, v in FOO_ATTR_TO_KEY.items()}

def dict_to_foo(dict_config: dict):
    kwargs = {
        FOO_KEY_TO_PARAM.get(key, key): value
        for key, value in dict_config.items()
    }
    return Foo(**kwargs)

def foo_to_dict(foo: Foo):
    return {
        FOO_ATTR_TO_KEY.get(name, name): value
        for name, value in vars(foo).items()
    }
user_12229510

There is a slightly cleaner way you can do this.

You can update the internal state of an object in python as by default it uses a dict.

Take for example

a1 = {"attr_1": "qack", "attr_2": 10}
a2 = {"attr_1": "woof"}
a3 = {"name": "John", "health": -10}

And a class

class Foo:
    def __init__(self, **attrs):
        self.__dict__.update(attrs)

Now we can upack the dicts and pass them into the constructor like such:

f1 = Foo(**a1)
print(f1.__dict__) # {'attr_1': 'qack', 'attr_2': 10}
f2 = Foo(**a2)
print(f2.__dict__) # {'attr_1': 'woof'}
f3 = Foo(**a3)
print(f3.__dict__) # {'name': 'John', 'health': -10}

print(f2.attr_1) # woof
print(f3.name) # John

This gives you the same functionality with less overhead code that you need to write.

user_191348380
Related