How to fix Python Django TypeError

Question

I have a simple model class which I want to return the the value for a field in my Django Admin.

Error Logs from terminal

TypeError: __str__ returned non-string (type NoneType)

models.py

class Solution(models.Model):
    description = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    error = models.ForeignKey(Error, on_delete=models.CASCADE)

    def __str__(self):
        return self.error + " fixed by " + self.user

coderboy · Accepted Answer · 2020-11-26 11:19:39Z

1

I already figured out the solution. Replacing the Solution Model Class to the below code snippet will fix the error.

models.py

class Solution(models.Model):
    description = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    error = models.ForeignKey(Error, on_delete=models.CASCADE)

    def __str__(self):
        return "Solution for " + str(self.error) + " by " + str(self.user)

answered Nov 26, 2020 at 11:19

coderboy

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1 Comment

user13255031 Over a year ago

Thanks, your solution came just in time

willeM_ Van Onsem · Accepted Answer · 2020-11-26 11:26:38Z

1

It is often better to make use of string formatting [pep-498] or literal string interpolation [pep-498], since this is a more robust tool that will automatically call str(…). Finally it is also more readable:

class Solution(models.Model):
    description = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    error = models.ForeignKey(Error, on_delete=models.CASCADE)

    def __str__(self):
        return f'{self.error} fixed by {self.user}'

answered Nov 26, 2020 at 11:26

willeM_ Van Onsem

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