How to use a dot “.” to access members of dictionary?

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Question :

How to use a dot “.” to access members of dictionary?

How do I make Python dictionary members accessible via a dot “.”?

For example, instead of writing mydict['val'], I’d like to write mydict.val.

Also I’d like to access nested dicts this way. For example

mydict.mydict2.val 

would refer to

mydict = { 'mydict2': { 'val': ... } }
Asked By: bodacydo

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Answer #1:

You can do it using this class I just made. With this class you can use the Map object like another dictionary(including json serialization) or with the dot notation. I hope to help you:

class Map(dict):
    """
    Example:
    m = Map({'first_name': 'Eduardo'}, last_name='Pool', age=24, sports=['Soccer'])
    """
    def __init__(self, *args, **kwargs):
        super(Map, self).__init__(*args, **kwargs)
        for arg in args:
            if isinstance(arg, dict):
                for k, v in arg.iteritems():
                    self[k] = v

        if kwargs:
            for k, v in kwargs.iteritems():
                self[k] = v

    def __getattr__(self, attr):
        return self.get(attr)

    def __setattr__(self, key, value):
        self.__setitem__(key, value)

    def __setitem__(self, key, value):
        super(Map, self).__setitem__(key, value)
        self.__dict__.update({key: value})

    def __delattr__(self, item):
        self.__delitem__(item)

    def __delitem__(self, key):
        super(Map, self).__delitem__(key)
        del self.__dict__[key]

Usage examples:

m = Map({'first_name': 'Eduardo'}, last_name='Pool', age=24, sports=['Soccer'])
# Add new key
m.new_key = 'Hello world!'
# Or
m['new_key'] = 'Hello world!'
print m.new_key
print m['new_key']
# Update values
m.new_key = 'Yay!'
# Or
m['new_key'] = 'Yay!'
# Delete key
del m.new_key
# Or
del m['new_key']
Answered By: epool

Answer #2:

I’ve always kept this around in a util file. You can use it as a mixin on your own classes too.

class dotdict(dict):
    """dot.notation access to dictionary attributes"""
    __getattr__ = dict.get
    __setattr__ = dict.__setitem__
    __delattr__ = dict.__delitem__

mydict = {'val':'it works'}
nested_dict = {'val':'nested works too'}
mydict = dotdict(mydict)
mydict.val
# 'it works'

mydict.nested = dotdict(nested_dict)
mydict.nested.val
# 'nested works too'
Answered By: derek73

Answer #3:

Install dotmap via pip

pip install dotmap

It does everything you want it to do and subclasses dict, so it operates like a normal dictionary:

from dotmap import DotMap

m = DotMap()
m.hello = 'world'
m.hello
m.hello += '!'
# m.hello and m['hello'] now both return 'world!'
m.val = 5
m.val2 = 'Sam'

On top of that, you can convert it to and from dict objects:

d = m.toDict()
m = DotMap(d) # automatic conversion in constructor

This means that if something you want to access is already in dict form, you can turn it into a DotMap for easy access:

import json
jsonDict = json.loads(text)
data = DotMap(jsonDict)
print data.location.city

Finally, it automatically creates new child DotMap instances so you can do things like this:

m = DotMap()
m.people.steve.age = 31

Comparison to Bunch

Full disclosure: I am the creator of the DotMap. I created it because Bunch was missing these features

  • remembering the order items are added and iterating in that order
  • automatic child DotMap creation, which saves time and makes for cleaner code when you have a lot of hierarchy
  • constructing from a dict and recursively converting all child dict instances to DotMap
Answered By: Chris Redford

Answer #4:

Derive from dict and and implement __getattr__ and __setattr__.

Or you can use Bunch which is very similar.

I don’t think it’s possible to monkeypatch built-in dict class.

Answered By: Kugel

Answer #5:

Fabric has a really nice, minimal implementation. Extending that to allow for nested access, we can use a defaultdict, and the result looks something like this:

from collections import defaultdict

class AttributeDict(defaultdict):
    def __init__(self):
        super(AttributeDict, self).__init__(AttributeDict)

    def __getattr__(self, key):
        try:
            return self[key]
        except KeyError:
            raise AttributeError(key)

    def __setattr__(self, key, value):
        self[key] = value

Make use of it as follows:

keys = AttributeDict()
keys.abc.xyz.x = 123
keys.abc.xyz.a.b.c = 234

That elaborates a bit on Kugel’s answer of “Derive from dict and and implement __getattr__ and __setattr__“. Now you know how!

Answered By: Dave

Answer #6:

I tried this:

class dotdict(dict):
    def __getattr__(self, name):
        return self[name]

you can try __getattribute__ too.

make every dict a type of dotdict would be good enough, if you want to init this from a multi-layer dict, try implement __init__ too.

Answered By: tdihp

Answer #7:

Use SimpleNamespace:

>>> from types import SimpleNamespace   
>>> d = dict(x=[1, 2], y=['a', 'b'])
>>> ns = SimpleNamespace(**d)
>>> ns.x
[1, 2]
>>> ns
namespace(x=[1, 2], y=['a', 'b'])
Answered By: Dmitry Zotikov

Answer #8:

I recently came across the ‘Box‘ library which does the same thing.

Installation command : pip install python-box

Example:

from box import Box

mydict = {"key1":{"v1":0.375,
                    "v2":0.625},
          "key2":0.125,
          }
mydict = Box(mydict)

print(mydict.key1.v1)

I found it to be more effective than other existing libraries like dotmap, which generate python recursion error when you have large nested dicts.

link to library and details: https://pypi.org/project/python-box/

Answered By: Pradip Gupta

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