fields.py 文件源码

def output_field(self):
        '''
        The type of field used to Cast/Coalesce to.

        Mainly because a max_length argument is required for CharField
        until this PR is merged: https://github.com/django/django/pull/8758
        '''
        Field = self.original_field.__class__
        if isinstance(self.original_field, fields.CharField):
            return Field(max_length=self.original_field.max_length)

        return Field()