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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).

>>> from istruct import istruct
>>> 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.

>>> p = person(first_name="Jim", last_name="Raynor", middle_name="Eugene")
>>> p
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.

>>> p.first_name
'Jim'
>>> p.dob
'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.

>>> p.first_name = "James"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute
>>> del p.email
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't delete attribute

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

>>> p = person("Jim", "Raynor")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/microamp/src/microamp/istruct/istruct/__init__.py", line 52, in _istruct
    "(%d found)" % (len(positional),))
TypeError: No positional arguments are allowed in istruct (2 found)

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

>>> p = person(last_name="Raynor")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/microamp/src/microamp/istruct/istruct/__init__.py", line 56, in _istruct
    return nt(**merge_dicts(kwargs, attrs))
TypeError: __new__() missing 1 required positional argument: 'first_name'

Versions Tested

  • Python 2.7
  • Python 3.2
  • Python 3.3
  • Python 3.4
  • Python 3.5
  • Python 3.6
  • PyPy
  • PyPy3

TODO

  • Find ways to annotate types

License

MIT

Release history Release notifications

This version
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0.1.6

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0.1.5

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0.1.3

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0.1.2

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0.1.1

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0.1

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