Add use cases example

examples/miniapps/use_cases/README.rst

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+Dependency Injector Use Cases example
+=====================================
+
+Instructions for running
+
+.. code-block:: bash
+
+    python run.py prod example@example.com
+    python run.py test example@example.com

examples/miniapps/use_cases/containers.py

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+"""Dependency injection containers for 'Use Cases' example application."""
+
+from dependency_injector import containers, providers
+
+from example.adapters import SmtpEmailSender, EchoEmailSender
+from example.use_cases import SignupUseCase
+
+
+class Adapters(containers.DeclarativeContainer):
+    """Adapters container."""
+
+    email_sender = providers.Singleton(SmtpEmailSender)
+
+
+class TestAdapters(containers.DeclarativeContainer):
+    """Adapters container.
+
+    This container is used for testing purposes.
+    """
+
+    email_sender = providers.Singleton(EchoEmailSender)
+
+
+class UseCases(containers.DeclarativeContainer):
+    """Use cases container."""
+
+    adapters = providers.DependenciesContainer()
+
+    signup = providers.Factory(SignupUseCase,
+                               email_sender=adapters.email_sender)

examples/miniapps/use_cases/example/__init__.py

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+"""Example top-level package."""

examples/miniapps/use_cases/example/adapters.py

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+"""Example adapters package."""
+
+
+class EmailSender(object):
+    """Abstract email sender."""
+
+    def send(self, to, body):
+        """Send email to specified email."""
+        raise NotImplementedError()
+
+
+class SmtpEmailSender(object):
+    """SMTP email sender uses SMTP protocol for sending emails."""
+
+    def send(self, to, body):
+        """Send email to specified email."""
+        # Send email via SMTP
+
+
+class EchoEmailSender(object):
+    """Echo email sender prints emails to stdout."""
+
+    def send(self, to, body):
+        """Send email to specified email."""
+        print('Sending email to "{0}", body = "{1}"'.format(to, body))

examples/miniapps/use_cases/example/use_cases.py

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+"""Example use cases package."""
+
+
+class UseCase(object):
+    """Abstract use case."""
+
+    def execute(self):
+        """Execute use case handling."""
+        raise NotImplementedError()
+
+
+class SignupUseCase(object):
+    """Sign up use cases registers users."""
+
+    def __init__(self, email_sender):
+        """Initializer."""
+        self.email_sender = email_sender
+
+    def execute(self, email):
+        """Execute use case handling."""
+        print('Sign up user {0}'.format(email))
+        self.email_sender.send(email, 'Welcome, "{}"'.format(email))

examples/miniapps/use_cases/run.py

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+"""Run 'Use Cases' example application."""
+
+import sys
+
+from containers import Adapters, TestAdapters, UseCases
+
+
+if __name__ == '__main__':
+    environment, email = sys.argv[1:]
+
+    if environment == 'prod':
+        adapters = Adapters()
+    elif environment == 'test':
+        adapters = TestAdapters()
+
+    use_cases = UseCases(adapters=adapters)
+
+    use_case = use_cases.signup()
+    use_case.execute(email)