When creating a Python application, the way its codebase is structured can play a significant role in the application's maintainability and ease of development. There is no one-size-fits-all answer to the best project structure; however, there are common practices and layouts that can be adapted based on the size and complexity of the project.

Basic Project Structure

For smaller or simpler projects, a basic structure often suffices. Here's a simple example of a basic Python project structure:

1my_project/
2│
3├── README.md          # Project description and instructions
4├── requirements.txt   # Project dependencies
5├── setup.py           # Installation script
6├── my_project/         # Main source code directory
7│   ├── __init__.py    # Makes the directory a Python package
8│   └── script.py      # A Python file with your actual code
9└── tests/              # Directory for test files
10    └── test_script.py  # Test file

Advanced Structure

For larger applications, particularly those involving multiple modules, a more intricate structure can help manage complexity effectively:

1my_project/
2│
3├── README.md
4├── requirements.txt
5├── setup.py
6├── my_project/
7│   ├── __init__.py
8│   ├── module1/
9│   │   ├── __init__.py
10│   │   └── file1.py   
11│   ├── module2/
12│   │   ├── __init__.py
13│   │   └── file2.py
14│   └── main.py         # Entry point of the application
15├── docs/               # Documentation files
16│   └── index.md
17├── tests/
18│   ├── __init__.py
19│   ├── test_module1.py
20│   └── test_module2.py
21└── scripts/            # Helper scripts
22    └── setup_db.py

Key Components Explained

1. README.md: This markdown file includes vital information about the project, including how to install and run the application.
2. requirements.txt: Lists all Python libraries that your project depends on.
3. setup.py: Contains setup configuration for installing the project as a package, making it reusable or distributable.
4. docs/: Holds the project documentation, which can be crucial for larger projects.
5. tests/: Contains the unit tests for your application, which are essential for automated testing and continuous integration.

Using a src Folder

Some developers prefer using a src folder to separate source code from other configuration and documentation files. This can be particularly useful in very large projects to keep Python code isolated from other parts of the project structure:

1my_project/
2│
3├── README.md
4├── requirements.txt
5├── setup.py
6├── src/
7│   └── my_project/
8│       ├── __init__.py
9│       ├── module1/
10│       │   ├── __init__.py
11│       │   └── file1.py   
12│       ├── module2/
13│       │   ├── __init__.py
14│       │   └── file2.py
15│       └── main.py
16├── docs/
17│   └── index.md
18├── tests/
19│   ├── __init__.py
20│   ├── test_module1.py
21│   └── test_module2.py
22└── scripts/
23    └── setup_db.py

Table Summarizing the Structures

Conclusion

The "best" project structure depends heavily on your specific project's needs, team size, and future plans for maintenance and scalability. Smaller projects might benefit from simplicity, while larger, more complex projects might require a more hierarchical structure with separated directories for different aspects of the project, including documentation, tests, and scripts.

Regardless of the structure you choose, ensure that it promotes clarity and minimizes the time new developers spend understanding how to work with your code. Always remember to update documentation and tests as your project evolves.