How to Correctly Pass Variables in URL_for to a Python Function in Flask

This guide provides a detailed guide on how to pass variables using URL_for in a Flask application, specifically addressing the common error of missing arguments in the function call.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Pass variable in url_for to Python function

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Correctly Pass Variables in URL_for to a Python Function in Flask

When working with Flask, it’s common to create buttons or links that trigger functions based on user interaction. One popular scenario is displaying a "Tickets" button associated with a project in your application, which when clicked, should retrieve tickets related to that project. However, you might encounter issues while trying to pass variables to the function that handles this action.

In this post, we will identify the problem of passing variables in the url_for method and provide a clear solution.

The Problem

In your Flask project, you attempted to create a button that should pass a project's ID to a function when clicked. The button in question uses the following Jinja syntax:

[[See Video to Reveal this Text or Code Snippet]]

However, when clicking this button, you received an error message stating:

[[See Video to Reveal this Text or Code Snippet]]

This error indicates that the Flask routing system isn’t aware of how to handle this proj_id variable, and as a result, it cannot map it to the expected function parameter.

Solution: Adding a Route Variable

The issue can be resolved by ensuring that your Flask route accepts the proj_id as a variable. You can achieve this by modifying the route decorator of the function handling this request. Here's the step-by-step process:

Step 1: Modify the Route

You need to define the route for the tix function correctly. Update the function's route to include a variable type (in this case, an integer) that corresponds with the proj_id parameter.

Here’s how you need to define your route:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Testing the Button

Summary

To prevent the TypeError and ensure the button correctly passes the project ID:

Define your Flask route to accept the required variable.

Use the url_for function correctly in your HTML.

Test to ensure the value being passed is valid.

By following these steps, you can effectively manage URL parameters in Flask applications and enhance user interaction with your software.

With this implementation, users can now easily access the ticket details related to specific projects without running into errors. Happy coding!