tarball.tar.gz

POSTGRES_USER

POSTGRES_PASSWORD

POSTGRES_HOSTNAME

APPLICATION_DB

POSTGRES_PORT

POSTGRES_DB

Python Execution

Flask

Flask + Postgres

Python Test

Clean architecture is a software design methodology that separates the processes of an application into discrete steps instead of presenting them as “spaghetti code.” With the versatility of Python, software engineers can build performant, modular applications quickly using the Flask framework.

This course will help you build better applications using the principles of clean architecture. You’ll start with an introduction to data flow in clean systems and learn about the advantages of layered architectures. Next, you’ll learn system components and the connections between application layers. You’ll then design and build a clean system using Python by layering components in guided coding exercises. Finally, you’ll learn how to add functional components for the web, handle errors, and work with external databases using both Postgres and MongoDB. At each step, you’ll use test-driven development practices to ensure robust functionality.

Clean Architecture in Python

## Exception from the previous lesson

If we run the Flask development web server now and try to access the `/rooms` endpoint, we’ll get the following response:

```
{"type": "SystemError", "message": "TypeError: list() got an unexpected keyword argument 'filters'"}
```

The HTTP 500 error we see in the HTTP response is exactly the same as the mapping of our `SystemError` use case error, which in turn signals a Python exception.

## Update the repository

This error comes from the repository, which hasn’t been migrated to the new API. To tackle this, we need to change the `list` method of the `MemRepo` class so that it accepts the `filters` parameter and acts accordingly. This is a critical step. The `filters` may have been considered part of the business logic and implemented in the use case itself. Still, we decided to leverage what the storage system can do, so we moved to filter in that external system. 

This is a reasonable choice to make because databases can usually perform filtering and ordering very well. Even though the in-memory storage we’re currently using isn’t a database, we’re preparing to use real external storage.

### Impact test case

The new version of repository tests is as follows:

# Exception from the previous lesson

If we run the Flask development web server now and try to access the `/rooms` endpoint, we’ll get the following response:

```
{"type": "SystemError", "message": "TypeError: list() got an unexpected keyword argument 'filters'"}
```

The HTTP 500 error we see in the HTTP response is exactly the same as the mapping of our `SystemError` use case error, which in turn signals a Python exception.

# Update the repository

This error comes from the repository, which hasn’t been migrated to the new API. To tackle this, we need to change the `list` method of the `MemRepo` class so that it accepts the `filters` parameter and acts accordingly. This is a critical step. The `filters` may have been considered part of the business logic and implemented in the use case itself. Still, we decided to leverage what the storage system can do, so we moved to filter in that external system. 

This is a reasonable choice to make because databases can usually perform filtering and ordering very well. Even though the in-memory storage we’re currently using isn’t a database, we’re preparing to use real external storage.

## Impact test case

The new version of repository tests is as follows:

Let’s learn the role of the repository in clean architecture.

Get Started

A Day in the Life of a Clean System

Components of Clean Architecture

A Simple Coding Example

Add a Web Application

Error Management

Integration with a Real External System Postgres

Integration with a Real External System MongoDB

Run a Production-ready System

Appendix

The Repository

Exception from the previous lesson

Update the repository

Impact test case