Why Does My Flask View Raise a TypeError: 'bool' Object is Not Callable?

Flask View Raising TypeError: 'bool' Object Not Callable

When developing Flask applications, you may encounter an error stating "TypeError: 'bool' object is not callable." This typically occurs when a view function returns a boolean value, which is not a valid response in Flask.

Understanding Flask View Responses

Flask views can return one of the following types of responses:

• String
• Response object or subclass
• Tuple of (string, status, headers) or (string, status)
• Valid WSGI application

The Issue

In the provided case, the view function returns True when a user successfully logs in. However, a boolean value is not a valid response type in Flask. As a result, Flask interprets the returned value as a WSGI application, leading to the error.

Solution

To resolve this issue, ensure that your view function returns one of the accepted response types. In this case, you can simply return a Response object to indicate a successful login:

from flask import Response

@app.route('/login', methods=['POST'])
def login():
    username = request.form['username']
    user = User.query.filter_by(username=username).first()

    if user:
        login_user(user)
        return Response(status=200)  # Successful login

    return Response(status=401)  # Unsuccessful login

By returning a Response object with the appropriate status code, you can resolve the TypeError and ensure that your view function handles user login correctly.

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