How to only accept a certain file type in FileField with Python Django?

To only accept a certain file type in FileField with Python Django, we can add a validator function to check the file extension.

For instance, we write

def validate_file_extension(value):
    import os
    from django.core.exceptions import ValidationError
    ext = os.path.splitext(value.name)[1]  # [0] returns path+filename
    valid_extensions = ['.pdf', '.doc', '.docx', '.jpg', '.png', '.xlsx', '.xls']
    if not ext.lower() in valid_extensions:
        raise ValidationError('Unsupported file extension.')

class Document(models.Model):
    file = models.FileField(upload_to="documents/%Y/%m/%d", validators=[validate_file_extension])

to define the validate_file_extension function to check the file extension of the selected file’s path.

We get the extension from the path with os.path.splitext(value.name)[1].

And then we check if the ext extension is in valid_extensions.

If it’s not, then we raise a ValidationError.

Next, in our Document model, we add a FileField with the validators arguments set to an array with the validate_file_extension as the value.

Then validate_file_extension when a file is uploaded.