scope-py 0.1.0

A lens library which targets usability over rigor.

Scope

Scope is a Python library inspired by optics from functional programming. The aim of Scope is to make various flavors of optics natural tools for Python programmers without requiring knowledge of the underlying math. Put simply, optics provide an abstraction for focusing on ("getting") and manipulating ("setting") data within larger and potentially nested structures.

This library favors usability over rigor and makes some decisions which increase utility at the expense of overloading and extending established terminology. For example, traversals in the standard usage, provide a means of focusing on multiple parts of a datastructure but do not provide similar setting behavior, whereas instances of the scope.Traversal class do provide a way to set multiple parts of a larger datastructure.

Introduction

The Scope library targets manipulation of JSON-like nested structures, which in Python are built from dictionaries, and lists, but custom optics are definable. Scope has a few classes you should be aware of;

• Lens: Base class providing get and put methods. Can be composed with other lenses.
• ParallelLens: Allows multiple lenses to be used in parallel.
• Traversal: Provides functionality for working with sequences of data.
• ItemLens: A lens focused on a specific item in an object which implements the __getitem__ dunder method.
• CRUDLens: An extension of a Lens that includes create and delete methods.
• ParallelCRUDLens: Allows multiple CRUD lenses to be used in parallel.
• CRUDTraversal: Extension of the CRUDLens for working with sequences of data.

Importantly, a Lens focuses on one thing and a Traversals focuses on many things. A CRUDLens extends the get/put functionality of lenses with additional create/delete functionality.

Usage

Basic lens composition example:

import scope

# create a lens that focuses on item 'b' after item 'a'
lens = scope.id['a']['b']
# lens = scope.compose_lenses(scope.id['a'], scope.id['b']) <-- alt. syntax

data = {'a': {'b': 3}}

# note -- lens(data) is an alias for lens.get(data)
assert lens(data) == 3
assert lens.put(4)(data) == {'a': {'b': 4}}

CRUDTraversal example:

lens = CRUDTraversal(ItemCRUDLens('a'), ItemCRUDLens('c'))
# lens = ItemCRUDLens('a')[::]['c'] <-- alt. syntax

data = {'a': [{'b': 1}, {'b': 3}]}

# "{'a': [{'b': 1, 'c': 2}, {'b': 3, 'c': 4}]}"
print(lens.create([2, 4])(data))

Custom attribute lens example:

# create a lens that gets/sets the attribute "my_attr" on an object
my_attr_lens = scope.Lens(lambda data: getattr(data, 'my_attr'), lambda value: lambda data: setattr(data, 'my_attr', value))

Parallel lens example:

x_lens, y_lens = scope.id['x'], scope.id['y']

# create a lens which focuses on 'x' and 'y' in parallel
parallel_lens = x_lens | y_lens
# parallel_lens = scope.ParallelLens(x_lens, y_lens) <-- alt. syntax

data = {'x': 2, 'y': 3}

assert sum(parallel_lens(data)) == 5

License

This project is open-sourced under the MIT license. See LICENSE for more information.

Contact

For questions or issues, please open an issue on GitHub.