Building an Automatic Code Formatter with Python

Introduction
Prerequisites
Setup
Creating the Code Formatter
Usage Examples
Common Errors and Troubleshooting
Tips and Tricks
Conclusion

Introduction

In this tutorial, you will learn how to build an automatic code formatter using Python. The code formatter will take a source code file as input and automatically format it according to specified rules, improving code readability and maintainability. By the end of this tutorial, you will have a functioning code formatter that you can use in your own projects.

Prerequisites

To follow this tutorial, you should have a basic understanding of Python programming language syntax and concepts. You should also have Python installed on your machine.

Setup

Before we begin, make sure you have the necessary packages installed. We will be using the black library, which is a popular code formatter for Python. Install it by running the following command in your terminal: pip install black

Creating the Code Formatter

Import the necessary libraries
```
import black
```
Define the format_code function

In this step, we will define the format_code function that takes a file path as input and formats the code in the file. We will use the black library’s format_file_in_place function to perform the code formatting.
```
def format_code(file_path):
    try:
        black.format_file_in_place(file_path)
        print(f"Code formatted successfully: {file_path}")
    except Exception as e:
        print(f"Error formatting code: {e}")
```
The format_file_in_place function takes care of reading the file, formatting the code, and writing the changes back to the file.
Test the code formatter

Now, let’s test the code formatter by calling the format_code function with a sample file path.
```
format_code("path/to/your/file.py")
```
Replace "path/to/your/file.py" with the actual file path you want to format. If the formatting is successful, you will see the message “Code formatted successfully” along with the file path. If there is an error, you will see the error message.

Handle multiple file paths

To allow the code formatter to handle multiple file paths at once, modify the format_code function as follows:

def format_code(*file_paths):
    try:
        for file_path in file_paths:
            black.format_file_in_place(file_path)
            print(f"Code formatted successfully: {file_path}")
    except Exception as e:
        print(f"Error formatting code: {e}")

Now, you can pass multiple file paths to the format_code function:

format_code("path/to/file1.py", "path/to/file2.py", "path/to/file3.py")

The code formatter will format each file separately.

Customizing formatting options

black library provides various options to customize the code formatting. You can define a pyproject.toml file in the project directory to specify the formatting options. Refer to the black library documentation for more details on the available formatting options.

Usage Examples

Format a single file

To format a single file, call the format_code function with the file path:
```
format_code("path/to/your/file.py")
```
The code in the file will be automatically formatted.
Format multiple files

If you have multiple files to format, pass their paths as separate arguments to the format_code function:
```
format_code("path/to/file1.py", "path/to/file2.py", "path/to/file3.py")
```
The code in each file will be formatted individually.

Common Errors and Troubleshooting

SyntaxError: unexpected EOF while parsing

This error occurs when there is a missing closing bracket or parenthesis in the code. Make sure to check the code for any missing brackets or parentheses and fix them before running the code formatter.
IndentationError: unindent does not match any outer indentation level

This error occurs when the indentation in the code is inconsistent. Ensure that the code follows a consistent indentation style before running the code formatter.
black.InvalidInput

This error occurs when the input file or directory is not found. Double-check the file path and ensure it is correct.

Tips and Tricks

Use the --check option with black to check if the code complies with the formatting rules without actually modifying the code. This can be useful in a CI/CD pipeline to enforce code formatting standards.
Integrate the code formatter into your development workflow by adding a pre-commit hook to automatically format the code before committing changes to version control.
Configure the pyproject.toml file to set the desired code formatting options according to your project’s style guide.

Conclusion

In this tutorial, you learned how to build an automatic code formatter using Python. We used the black library to format the code and demonstrated how to format single and multiple files. We also covered common errors, troubleshooting tips, and provided some additional tips and tricks. You can now incorporate this code formatter into your own projects to improve code readability and maintainability. Happy coding!

Please note that this is just a sample tutorial. The tutorial can be expanded and enhanced with more code samples, explanations, and advanced features.

Published: 26 October 2019