PyJudo

Overview

PyJudo is a python library to support the dependency injection (DI) pattern. It facilitates the registration of services, resolves dependencies, and manages the lifecycle of services throughout your application. By decoupling service creation from business logic, PyJudo promotes cleaner, more maintainable, and testable codebases.

The goal of PyJudo is to provide a lightweight, easy-to-use and simple mechanism to let developers employ a dependency injection pattern into their application's implementation. It takes inspiration from the Microsoft .NET Dependency Injection library of providing a container for services.

It's as simple as:

• Define what a service does (e.g. with an abstract class) - this is the "interface"
• Create a service container
• Create a concrete implementation of the interface
• Register the concrete implementation against the interface with the container
• Retrieve an instance of the interface from the container
• (or specify the interface in another service's constructor)

Installation

PyJudo is available on PyPi; install using:

pip install pyjudo

Features

• Services container:

  • Provides a container to register and resolve dependencies.

• Service dependency injection:

  • Automatically resolves and injects dependencies for service (classes) retrieved from the service container.

• Callable dependency injection:

  • Automatically resolve dependencies for callables (functions, methods, class methods & static methods), decorated with @container.inject

• Service lifetimes:

  • Singleton: A single instance created and shared across the container.
  • Scoped: A single instance created and shared within a scope.
  • Transient: A new instance created every time the service is retrieved.

• Disposable services:

  • Automatically disposes of services that implement the Disposable protocol when a scope ends.
  • Provides an IDisposable abstract to safeguard against the use of "disposed" instances.

• Factories:

  • Registering services with factories, just register the callable.
  • Add dependencies as factories using Factory[MyService] in the constructor.

• Circular dependencies:

  • Detects and prevents circular dependencies during service resolution.

• Thread safety:

  • Ensures safe use in multi-threaded environments by managing scopes and service resolutions per thread.

• Context management

  • Supports the use of context managers (i.e. with ...) to manage service scopes and their respective service lifetimes.

Quick Start

The quick start example below gives a brief overview of using PyJudo; for a more in-depth guide, please see the Examples.

1. Define Interfaces and Implementations

Start by defining service interfaces (abstract classes) and their concrete implementations:

from abc import ABC, abstractmethod
from pyjudo import ServiceContainer

# Define service interfaces
class IDatabaseConnection(ABC):
    @abstractmethod
    def query(self, sql: str) -> Any: ...

class IDatabaseURIBuilder(ABC):
    @abstractmethod
    def get_uri(self) -> str: ...


# Implement the services
class DatabaseConnection(IDatabaseConnection):
    def __init__(self, uri_builder: IDatabaseURIBuilder, table_name="default"):
        self.connection_string = uri_builder.get_uri()
        self.table_name = table_name
        self.connected = True
        print(f"Connected to database: {self.connection_string}")

    def query(self, sql: str) -> Any:
        if not self.connected:
            raise Exception("Not connected to the database.")
        print(f"Executing query: {sql} FROM {self.table_name}")
        return {"result": "data"}

    def dispose(self) -> None:
        if self.connected:
            self.connected = False
            print(f"Disconnected from database: {self.connection_string}")

class TestDatabaseURIBuilder(IDatabaseURIBuilder):
    def get_uri(self):
        return "connect.to.me"

2. Register Services

Create an instance of the ServiceContainer and register your services with appropriate lifetimes:

# Create the service container
services = ServiceContainer()

# Register services
services.add_transient(IDatabaseURIBuilder, TestDatabaseURIBuilder)
services.add_scoped(IDatabaseConnection, DatabaseConnection)

3. Resolve Services

Retrieve and utilise services from the ServiceCollection. When retrieving services from the ServiceContainer, services referenced in constructors (__init__) will be automatically resolved.

Constructor arguments may also be overwritten when retrieving services from the container, i.e. table_name="foobar". (See 01 Basic).

Callables can have services injected using the @services.inject decorator. (See 05 Functions).

with services.create_scope() as service_scope:
    db = service_scope[IDatabaseConnection](table_name="foobar")
    result = db.query("SELECT *")
print(result)


@services.inject
def print_connection_str(db_uri_builder: IDatabaseURIBuilder):
    print("Database connection string:", db_uri_builder.get_uri())

print_connection_str()
# Output:
"""
Connected to database: connect.to.me
Executing query: SELECT * FROM foobar
Disconnected from database: connect.to.me
{'result': 'data'}
Database connection string: connect.to.me
"""