attrdict 0.5.1

A dict with attribute-style access

AttrDict is a 2.6, 2.7, 3-compatible dictionary that allows its elements to be accessed both as keys and as attributes:

> from attrdict import AttrDict
> a = AttrDict({'foo': 'bar'})
> a.foo
'bar'
> a['foo']
'bar'

With this, you can easily create convenient, heirarchical settings objects.

with open('settings.yaml', 'r') as fileobj:
    settings = AttrDict(yaml.safe_load(fileobj))

cursor = connect(**settings.db.credentials).cursor()

cursor.execute("SELECT column FROM table");

Installation

AttrDict is in PyPI, so it can be installed directly using:

$ pip install attrdict

Or from Github:

$ git clone https://github.com/bcj/AttrDict
$ cd AttrDict
$ python setup.py install

Documentation

Documentation is available at https://github.com/bcj/AttrDict

Usage

Creation

An empty AttrDict can be created with:

a = AttrDict()

Or, you can pass an existing dict (or other type of Mapping object):

a = AttrDict({'foo': 'bar'})

NOTE: Unlike dict, AttrDict will not clone on creation. AttrDict’s internal dictionary will be the same instance as the dict passed in.

Access

AttrDict can be used exactly like a normal dict:

> a = AttrDict()
> a['foo'] = 'bar'
> a['foo']
'bar'
> '{foo}'.format(**a)
'bar'
> del a['foo']
> a.get('foo', 'default')
'default'

AttrDict can also have it’s keys manipulated as attributes to the object:

> a = AttrDict()
> a.foo = 'bar'
> a.foo
'bar'
> del a.foo

Both methods operate on the same underlying object, so operations are interchangeable. The only difference between the two methods is that where dict-style access would return a dict, attribute-style access will return an AttrDict. This allows recursive attribute-style access:

> a = AttrDict({'foo': {'bar': 'baz'}})
> a.foo.bar
'baz'
> a['foo'].bar
AttributeError: 'dict' object has no attribute 'bar'

There are some valid keys that cannot be accessed as attributes. To be accessed as an attribute, a key must:

• be a string

• start with an alphabetic character

• be comprised solely of alphanumeric characters and underscores

• not map to an existing attribute name (e.g., get, items)

To access these attributes while retaining an AttrDict wrapper (or to dynamically access any key as an attribute):

> a = AttrDict({'_foo': {'bar': 'baz'}})
> a('_foo').bar
'baz'

Merging

AttrDicts can be merged with eachother or other dict objects using the + operator. For conflicting keys, the right dict’s value will be preferred, but in the case of two dictionary values, they will be recursively merged:

> a = {'foo': 'bar', 'alpha': {'beta': 'a', 'a': 'a'}}
> b = {'lorem': 'ipsum', 'alpha': {'bravo': 'b', 'a': 'b'}}
> AttrDict(a) + b
{'foo': 'bar', 'lorem': 'ipsum', 'alpha': {'beta': 'a', 'bravo': 'b', 'a': 'b'}}

NOTE: AttrDict’s add is not commutative, a + b != b + a:

> a = {'foo': 'bar', 'alpha': {'beta': 'b', 'a': 0}}
> b = {'lorem': 'ipsum', 'alpha': {'bravo': 'b', 'a': 1}}
> b + AttrDict(a)
{'foo': 'bar', 'lorem': 'ipsum', 'alpha': {'beta': 'a', 'bravo': 'b', 'a': }}

Sequences

By default, items in non-string Sequences (e.g. lists, tuples) will be converted to AttrDicts:

> adict = AttrDict({'list': [{'value': 1}, 'value': 2]})
> for element in adict.list:
>     element.value
1
2

This will not occur if you access the AttrDict as a dictionary:

> adict = AttrDict({'list': [{'value': 1}, 'value': 2]})
> for element in adict['list']:
>     isinstance(element, AttrDict)
False
False

To disable this behavior globally, pass the attribute recursive=False to the constructor:

> adict = AttrDict({'list': [{'value': 1}, 'value': 2]}, recursive=False)
> for element in adict['list']:
>     isinstance(element, AttrDict)
False
False

When merging an AttrDict with another mapping, this behavior will be disabled if at least one of the merged items is an AttrDict that has set recursive to False.

DefaultDict

AttrDict supports defaultdict-style automatic creation of attributes:

> adict = AttrDict(default_factory=list)
> adict.foo
[]

Furthermore, if pass_key=True, then the key will be passed to the function used when creating the value:

> adict = AttrDict(default_factory=lambda value: value.upper(), pass_key=True)
> adict.foo
'FOO'

load

A common usage for AttrDict is to use it in combination with settings files to create hierarchical settings. attrdict comes with a load function to make this easier:

from attrdict import load

settings = load('settings.json')

By default, load uses json.load to load the settings file, but this can be overrided by passing load_function=YOUR_LOAD_FUNCTION.

load supports loading from multiple files at once. This allows for overriding of default settings, e.g.:

from attrdict import load
from yaml import safe_load

# config.yaml =
# emergency:
#   email: [e-mail]
#   message: Something went wrong
#
# user.yaml =
# emergency:
#   email: [e-mail]
settings = load('config.yaml', 'user.yaml', load_function=safe_load)

assert settings.email == '[e-mail]'
assert settings.message == 'Something went wrong'

License

AttrDict is released under a MIT license.