How to Fix RuntimeError in Flask When Accessing request.form in a Class

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Understanding and Solving the RuntimeError in Flask

You might be building a small application, like a forex converter, which lets users convert one currency to another. The application is designed to take data from an HTML form and perform conversions based on the user input. However, when trying to access the form data through a class, you encounter the error:

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This error occurs when your code attempts to access the request object outside the context of an active request. Let's break down why this happens and how to solve it.

Why Does This Error Occur?

Solution: Correctly Managing the Request Context

To resolve this issue, you need to ensure that your class is instantiated within an active request context. Here’s how to approach the solution:

Step 1: Moving Object Initialization Inside a View Function

Instead of creating an instance of your Survey class at the global level, you should instantiate it within your Flask route function. This ensures that the request context is active:

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Step 2: Modifying the Constructor to Take Parameters

Although the above fix works, it's not ideal to access request directly in the class constructor. A better practice is to pass the necessary parameters directly to the constructor:

Updated Class Definition

Modify the Survey class to accept parameters in its constructor:

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Updated View Function

In the add_conversion function, pass the form data when instantiating Survey:

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Conclusion