Magicattr

A getattr and setattr that works on nested objects, lists, dictionaries, and any combination thereof without resorting to eval.

It differs from getattr and setattr in that it retains the failure cause instead of always raising an AttributeError.

Example

Say we have a person class as follows:

class Person:
    settings = {
        'autosave': True,
        'style': {
            'height': 30,
            'width': 200
        },
        'themes': ['light', 'dark']
    }
    def __init__(self, name, age, friends):
        self.name = name
        self.age = age
        self.friends = friends


bob = Person(name="Bob", age=31, friends=[])
jill = Person(name="Jill", age=29, friends=[bob])
jack = Person(name="Jack", age=28, friends=[bob, jill])

With magicattr we can do this

# Nothing new
assert magicattr.get(bob, 'age') == 31

# Lists
assert magicattr.get(jill, 'friends[0].name') == 'Bob'
assert magicattr.get(jack, 'friends[-1].age') == 29

# Dict lookups
assert magicattr.get(jack, 'settings["style"]["width"]') == 200

# Combination of lookups
assert magicattr.get(jack, 'settings["themes"][-2]') == 'light'
assert magicattr.get(jack, 'friends[-1].settings["themes"][1]') == 'dark'

# Setattr
magicattr.set(bob, 'settings["style"]["width"]', 400)
assert magicattr.get(bob, 'settings["style"]["width"]') == 400

# Nested objects
magicattr.set(bob, 'friends', [jack, jill])
assert magicattr.get(jack, 'friends[0].friends[0]') == jack

magicattr.set(jill, 'friends[0].age', 32)
assert bob.age == 32

You can also delete like this too.

# Deletion
magicattr.delete(jill, 'friends[0]')
assert len(jill.friends) == 0

magicattr.delete(jill, 'age')
assert not hasattr(jill, 'age')

magicattr.delete(bob, 'friends[0].age')
assert not hasattr(jack, 'age')

What if someone tries to mess with you?

# Unsupported
with pytest.raises(NotImplementedError) as e:
    magicattr.get(bob, 'friends[0+1]')

with pytest.raises(SyntaxError) as e:
    magicattr.get(bob, 'friends[')

with pytest.raises(ValueError) as e:
    magicattr.get(bob, 'friends = [1,1]')

# Nice try, function calls are not allowed
with pytest.raises(ValueError):
    magicattr.get(bob, 'friends.pop(0)')

Did I miss anything? Let me know!

What it can't do?

Slicing, expressions, function calls, append/pop from lists, eval stuff, etc...

How does it work?

Parses the attr string into an ast node and manually evaluates it.

Installing

pip install magicattr

License

MIT

Hope it helps, cheers!