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Immutable struct with sane defaults

Project description

Immutable struct built on top of collections.namedtuple with sane defaults

Goals

  • Immutable, dictionary-like data structure (Note: istruct is not an immutable version of the existing struct in Python)
  • Minimal
  • Support required and optional fields (with default values)
  • Strictly disallow positional arguments

Installation

pip install istruct

Quick Start

First, create an istruct object called person where first_name and last_name are required whereas middle_name, dob and email are optional (with default values specified).

In [1]: from istruct import istruct

In [2]: person = istruct("first_name", "last_name", middle_name="", dob="2000-01-01", email=None)

Then, create an instance of person with first_name, last_name and middle_name.

In [3]: p = person(first_name="Jim", last_name="Raynor", middle_name="Eugene")

In [4]: p
Out[4]: istruct(first_name='Jim', last_name='Raynor', email=None, dob='2000-01-01', middle_name='Eugene')

You can retrieve field values like you would normally do.

In [5]: p.first_name
Out[5]: 'Jim'

In [6]: p.dob
Out[6]: '2000-01-01'

p is immutable, meaning that it cannot be modified after created. Thus, set/delete operations like below would fail, raising an AttributeError.

In [7]: p.first_name = "James"
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-13-681faedb279a> in <module>()
----> 1 p.first_name = "James"

AttributeError: can't set attribute

In [8]: del p.email
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-12-d5c698764d13> in <module>()
----> 1 del p.email

AttributeError: can't delete attribute

istruct only accepts named/keyword arguments. It strictly disallows positional arguments by design.

In [9]: p = person("Jim", "Raynor")
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-c0bdbd269e9f> in <module>()
----> 1 p = person("Jim", "Raynor")

/home/microamp/devel/projs/istruct/istruct/__init__.py in _istruct(*positional, **attrs)
     49         if positional:
     50             raise TypeError("No positional arguments are allowed in istruct "
---> 51                             "(%d found)" % (len(positional),))
     52
     53         nt = namedtuple(__name__,

TypeError: No positional arguments are allowed in istruct (2 found)

istruct would raise a TypeError when one or more required fields are omitted.

In [10]: p = person(last_name="Raynor")
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-15-451d2add9ee8> in <module>()
----> 1 p = person(last_name="Raynor")

/home/microamp/devel/projs/istruct/istruct.py in _istruct(**attrs)
     25     def _istruct(**attrs):
     26         nt = namedtuple(name(), merge_tuples(args, tuple(kwargs.keys())))
---> 27         return nt(**merge_dicts(kwargs, attrs))
     28
     29     return _istruct

TypeError: __new__() missing 1 required positional argument: 'first_name'

Versions Tested

  • Python 2.7
  • Python 3.2
  • Python 3.3
  • Python 3.4
  • PyPy
  • PyPy3

TODO

  • Find ways to annotate types

License

MIT

Project details


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