Fixing OntoMermaid's `playground.py` Errors

Nov 14, 2025 by Admin 44 views

Fixing `playground.py` Run Instructions in OntoMermaid: A Comprehensive Guide

Hey guys! Ever tried running playground.py in OntoMermaid and hit a wall with errors? You're not alone! This guide breaks down those pesky TemplateNotFound and FileNotFoundError issues, giving you step-by-step instructions to get things running smoothly. Let's dive in!

Understanding the Errors

Before we get our hands dirty with solutions, let's understand the problems. You've likely encountered two main errors when trying to run playground.py:

jinja2.exceptions.TemplateNotFound: index.html: This error pops up when the Flask application can't find the index.html template file. Flask, the web framework used in playground.py, uses Jinja2 to render HTML templates. If Jinja2 can't locate the specified template, it throws this error. This usually means the application isn't looking in the right place for your HTML files.
FileNotFoundError: [Errno 2] No such file or directory: .../specification/mermaid.trig: This error occurs because the script is trying to read the mermaid.trig file, but it can't find it at the specified path. This typically happens when the script is executed from a different directory than expected, causing relative paths to resolve incorrectly. It's like telling someone to find your keys on the table, but they are actually on the counter! So, the path specified in the code to find the file mermaid.trig is not correct according to the location where the command is being executed.

Solution 1: Fixing `TemplateNotFound: index.html`

This error usually arises due to how Flask is configured to locate template files. Here's how to resolve it:

Verify Template Location: First, make sure index.html actually exists and is in the correct directory. By default, Flask looks for templates in a folder named templates within the application's root directory. If you haven't created this directory or placed index.html inside it, that's likely the problem.
Create the templates Directory: If it doesn't exist, create a directory named templates at the same level as your playground.py file. This is where Flask expects to find your HTML templates.
```
mkdir tools/playground/templates
```
Move index.html: Place index.html inside the templates directory. Ensure the file is named correctly and doesn't have any typos.
```
mv index.html tools/playground/templates/
```
Run from the Correct Directory: Ensure you're running the Flask application from the project's root directory. This ensures Flask can correctly resolve the path to the templates folder. The command should be executed from the root of your OntoMermaid repository:
```
uv run python tools/playground/playground.py
```
Configure Template Folder (if necessary): If your templates are in a different location, you might need to configure Flask to look in the correct directory. Although not usually required for standard setups, you can specify the template_folder when creating the Flask app. In playground.py, ensure you have something like this:
```
app = Flask(__name__, template_folder='templates')
```
This explicitly tells Flask to look for templates in the templates directory relative to the application's root.

Detailed Explanation

Let's get into the weeds a bit. When Flask initializes, it needs to know where to find your HTML templates. By default, it assumes these files are located in a directory named templates in the same directory as your main application file (in this case, playground.py).

So, if you're getting the TemplateNotFound error, it means Flask is looking for index.html in the wrong place. To fix this, you have two main options:

Option 1: The Standard Way: Create a templates folder in the same directory as playground.py and put index.html inside it. This is the easiest and most common approach.
Option 2: Custom Configuration: If you want to keep your templates somewhere else (maybe in a views folder or something), you need to tell Flask where to find them. You do this by setting the template_folder argument when you create your Flask app:
```
app = Flask(__name__, template_folder='/path/to/your/templates')
```
Replace /path/to/your/templates with the actual path to your template directory. Remember, the path should be relative to where you're running the script from, or an absolute path.

Solution 2: Fixing `FileNotFoundError: No such file or directory: .../specification/mermaid.trig`

This error typically arises from incorrect relative paths when the script is run from different locations. Here’s how to fix it:

Understand Relative Paths: The script uses a relative path to locate mermaid.trig. This means the path is relative to the directory from which you execute the script.
Run from the Correct Directory: The easiest solution is to run the script from the tools/playground directory. This ensures that the relative path specification/mermaid.trig correctly points to the file.
```
cd tools/playground
uv run python playground.py
```
Correct the File Path: Alternatively, you can modify the script to use an absolute path or a path relative to the project root. To use a path relative to the project root, you can adjust the directory_path variable.
```
import os

directory_path = os.path.join(os.path.dirname(os.path.dirname(os.path.dirname(__file__))), 'tools', 'playground')
mermaid_vocabulary = readStringFromFile(os.path.join(directory_path, 
```