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160 lines
4.7 KiB
Markdown
160 lines
4.7 KiB
Markdown
# Objects
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Dependency management tool for Python projects.
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[](https://pypi.python.org/pypi/Objects/)
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[](https://pypi.python.org/pypi/Objects/)
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[](https://travis-ci.org/rmk135/objects)
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[](https://coveralls.io/r/rmk135/objects)
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[](https://pypi.python.org/pypi/Objects/)
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[](https://pypi.python.org/pypi/Objects/)
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[](https://pypi.python.org/pypi/Objects/)
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## Introduction
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Python ecosystem consists of a big amount of various classes, functions and
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objects that could be used for applications development. Each of them has its
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own role.
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Modern Python applications are mostly the composition of well-known open
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source systems, frameworks, libraries and some turnkey functionality.
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When application goes bigger, its amount of objects and their dependencies
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also increased extremely fast and became hard to maintain.
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`Objects` is designed to be developer's friendly tool for managing objects
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and their dependencies in formal, pretty way. Main idea of `Objects` is to
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keep dependencies under control.
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## Entities
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Current section describes main `Objects` entities and their interaction.
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### Providers
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Providers are strategies of accessing objects.
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All providers are callable. They describe how particular objects will be
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provided. For example:
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```python
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"""`NewInstance` and `Singleton` providers example."""
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from objects.providers import NewInstance
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from objects.providers import Singleton
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# NewInstance provider will create new instance of specified class
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# on every call.
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new_object = NewInstance(object)
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object_1 = new_object()
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object_2 = new_object()
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assert object_1 is not object_2
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# Singleton provider will create new instance of specified class on first call,
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# and return same instance on every next call.
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single_object = Singleton(object)
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single_object_1 = single_object()
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single_object_2 = single_object()
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assert single_object_1 is single_object_2
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```
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### Injections
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Injections are additional instructions, that are used for determining
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dependencies of objects.
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Objects can take dependencies in various forms. Some objects take init
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arguments, other are using attributes or methods to be initialized. Injection,
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in terms of `Objects`, is an instruction how to provide dependency for the
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particular object.
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Every Python object could be an injection value. Special case is a `Objects`
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provider as an injection value. In such case, injection value is a result of
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injectable provider call (every time injection is done).
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Injections are used by providers.
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### Catalogs
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Catalogs are named set of providers.
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## Example
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```python
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"""Concept example of `Objects`."""
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from objects.catalog import AbstractCatalog
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from objects.providers import Singleton
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from objects.providers import NewInstance
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from objects.injections import KwArg
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from objects.injections import Attribute
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from objects.injections import inject
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import sqlite3
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class ObjectA(object):
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"""Example class ObjectA, that has dependency on database."""
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def __init__(self, db):
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"""Initializer."""
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self.db = db
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class ObjectB(object):
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"""Example class ObjectB, that has dependencies on ObjectA and database."""
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def __init__(self, a, db):
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"""Initializer."""
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self.a = a
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self.db = db
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class Catalog(AbstractCatalog):
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"""Catalog of objects providers."""
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database = Singleton(sqlite3.Connection,
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KwArg('database', ':memory:'),
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Attribute('row_factory', sqlite3.Row))
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""":type: (objects.Provider) -> sqlite3.Connection"""
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object_a = NewInstance(ObjectA,
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KwArg('db', database))
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""":type: (objects.Provider) -> ObjectA"""
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object_b = NewInstance(ObjectB,
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KwArg('a', object_a),
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KwArg('db', database))
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""":type: (objects.Provider) -> ObjectB"""
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# Catalog static provides.
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a1, a2 = Catalog.object_a(), Catalog.object_a()
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b1, b2 = Catalog.object_b(), Catalog.object_b()
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assert a1 is not a2
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assert b1 is not b2
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assert a1.db is a2.db is b1.db is b2.db is Catalog.database()
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# Example of inline injections.
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@inject(KwArg('a', Catalog.object_a))
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@inject(KwArg('b', Catalog.object_b))
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@inject(KwArg('database', Catalog.database))
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def example(a, b, database):
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assert a.db is b.db is database is Catalog.database()
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example()
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```
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