CleverDict

OVERVIEW

CleverDict is a hybrid Python data class which allows both object.attribute and dictionary['key'] notation to be used simultaneously and interchangeably. It's particularly handy when your code is mainly object-orientated but you want a 'DRY' and extensible way to import data in json/dictionary format into your objects... or vice versa... without having to write extra code just to handle the translation.

The class also optionally triggers a ._save() method (which you can adapt or overwrite) which it calls whenever an attribute or dictionary value is created or changed. This is especially useful if you want your object's values to be automatically pickled, encoded, saved to a file or database, uploaded to the cloud etc. without having to slavishly call your update function after every single operation where attributes (might) change.

INSTALLATION

No dependencies. Very lightweight:

pip install cleverdict

or to cover all bases...

python -m pip install cleverdict --upgrade --user

QUICKSTART

CleverDict objects behave like normal Python dictionaries, but with the convenience of immediately offering read and write access to their data (keys and values) using the object.attribute syntax, which many people find easier to type and more intuitive to read and understand.

1. BASIC USE

>>> from cleverdict import CleverDict
>>> x = CleverDict({'total':6, 'usergroup': "Knights of Ni"})

>>> x.total
6
>>> x['total']
6
>>> x.usergroup
'Knights of Ni'
>>> x['usergroup']
'Knights of Ni'

2. KEYWORD ARGUMENTS

You can also supply keyword arguments like this:

>>> x = CleverDict(created = "today", review = "tomorrow")

>>> x.created
'today'
>>> x['review']
'tomorrow'

Regardless of which syntax you use, new values are immediately available via both methods:

>>> x['life'] = 42
>>> x.life += 1
>>> x['life']
43

>>> del x['life']
>>> x.life
# KeyError: 'life'

3. NORMALISATION

By default CleverDict attempts to normalise keys such as " " and "" and strings with characters not normally allowed in object.attribute names. So for example 1 (integer) becomes "_1" (string):

>>> x = CleverDict({1: "One"})

>>> x._1
'One'
>>> x
CleverDict({'_1':'One'})

You can toggle this behaviour Off and On (for all future operations on all current and future objects of the class) as follows:

>>> CleverDict.normalise = False  # or: True
>>> x = CleverDict({1: "One"})

>>> hasattr(x, "_1")
False
>>> x
CleverDict({1:'One'})
>>> x[1]
'One'

4. IMPORTING DATA FROM OTHER OBJECTS

You can import an existing object's data (but not its methods) directly using vars():

x = CleverDict(vars(my_existing_object))

>>> list(x.items())
[('total', 6), ('usergroup', 'Knights of Ni'), ('life', 42)]

5. ENABLING THE AUTO-SAVE FUNCTION

You can set pretty much any function to run automatically whenever a CleverDict value is created or changed. There's an example function in cleverict.test_cleverdict which demonstrates this:

>>> from cleverdict.test_cleverdict import my_example_save_function
>>> CleverDict._save = my_example_save_function

>>> x = CleverDict({'total':6, 'usergroup': "Knights of Ni"})
Notional save to database: .total = 6 <class 'int'>
Notional save to database: .usergroup = Knights of Ni <class 'str'>

>>> x.life = 42
Notional save to database: .life = 42 <class 'int'>

The example function above also appends output to a file, which you might want for debugging, auditing, further analysis etc.:

>>> with open("example.log","r") as file:
...     log = file.read()

>>> log.splitlines()
["Notional save to database: .age = 10 <class 'int'>",
"Notional save to database: .total = 6 <class 'int'>",
"Notional save to database: .usergroup = Knights of Ni <class 'str'>"]

NB: The ._save() method is a class method, so changing CleverDict._save will apply the new ._save() method to all previously created CleverDict objects as well as future ones.

6. CREATING YOUR OWN AUTO-SAVE FUNCTION

When writing your own ._save() function, you'll need to specify three arguments as follows:

>>> def your_function(self, name: str = "", value: any = ""):
...     print("Ni!")

• self: because we're dealing with objects and classes...
• name: a valid Python .attribute name preferably, otherwise you'll only be able to access it using dictionary['key'] notation later on.
• value: anything

7. SETTING DIFFERENT AUTO-SAVE FUNCTIONS FOR DIFFERENT OBJECTS

If you want to specify different ._save() behaviours for different objects, consider creating sublasses that inherit from CleverDict and set a different ._save() function for each subclass e.g.:

>>> class Type1(CleverDict): pass
>>> Type1._save = my_save_function1

>>> class Type2(CleverDict): pass
>>> Type2._save = my_save_function2

8. CHANGING THE WAY CLEVERDICT OBJECTS ARE DISPLAYED

If you want to overwrite the __str__ method with your own function, or delete it so print() and str() default to __repr__ that's easy enough too:

>>> print(x)
.total = 6 <class 'int'>
.usergroup = Knights of Ni <class 'str'>

>>> def my__str__replacement(self):
...     return str(type(self))

>>> setattr(CleverDict, "__str__", my__str__replacement)
>>> print(x)
<class 'cleverdict.cleverdict.CleverDict'>

>>> delattr(CleverDict, "__str__")
>>> print(x)
CleverDict({'total':6, 'usergroup':'Knights of Ni'})

CONTRIBUTING

We'd love to see Pull Requests (and relevant tests) from other contributors, particularly if you can help with the following:

1. It would be great if CleverDict behaviour could be easily 'grafted on' to existing classes using inheritance, without causing recursion or requiring a rewrite/overwrite of the original class.

   For example if it were as easy as:

   >>> class MyDatetime(datetime.datetime, CleverDict):
   ...     pass
   
   >>> mdt = MyDatetime.now()
   >>> mdt.hour
   4
   >>> mdt['hour']
   4
   

CREDITS

CleverDict was developed jointly by Peter Fison, Ruud van der Ham, Loic Domaigne, and Rik Huygen who met on the friendly and excellent Pythonista Cafe forum (www.pythonistacafe.com). Peter got the ball rolling after noticing a super-convenient, but not fully-fledged feature in Pandas that allows you to (mostly) use object.attribute syntax or dictionary['key'] syntax interchangeably. Ruud, Loic and Rik then started swapping ideas for a hybrid dictionary/data class based on UserDict and the magic of __getattr__ and __setattr__, and CleverDict was born*.

(*) CleverDict was originally called attr_dict but several confusing flavours of this and AttrDict exist on PyPi and Github already. Hopefully the new name raises a wry smile as well as being more memorable...