Why Does My Flask App Throw a `TemplateNotFound` Error, Even Though My Template File Exists?

Troubleshooting Flask's TemplateNotFound Error

When attempting to render a template in Flask, such as 'home.html', you may encounter the 'jinja2.exceptions.TemplateNotFound' error despite the existence of the file. Understanding why this occurs and resolving the issue is crucial for successful template rendering.

Cause:

The primary reason for this error is that Flask cannot locate the specified template file in its default template directory, which is 'templates'. By default, Flask looks for templates in this subdirectory alongside the Python module where the Flask app is defined.

Solution:

Ensure that the 'home.html' template is placed in the correct location. It should be in the 'templates' subdirectory adjacent to the Python module.

Additional Considerations:

• If the Flask app is a package, the 'templates' folder must be created within the package directory.
• If you have named your templates folder differently, you can specify its location using 'app.py'. For instance, 'app = Flask(__name__, template_folder='template')' would use the 'template' directory.
• Flask provides a 'EXPLAIN_TEMPLATE_LOADING' option to obtain detailed information about template search attempts. This can be helpful for debugging.

Example Template Structure:

• For a non-packaged app:

myproject/
    app.py
    templates/
        home.html

• For a packaged app:

myproject/
    mypackage/
        __init__.py
        templates/
            home.html

By following these guidelines, you can effectively resolve the TemplateNotFound error and render your templates as intended.

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