Django (1, 4, 0, 'alpha', 0): Trying to get custom model field to pass custom attribute to form (and eventually a widget)... What am I doing wrong here?

admin.py

from django.contrib import admin
from test.models import Test

admin.site.register(Test)

fields.py

from django.db import models
from test import forms

class TestField(models.CharField):
    
    """
    Docstring...
    """
    
    description = 'Description...'
    
    def __init__(self, baz=None, *args, **kwargs):
#     def __init__(self, *args, **kwargs):
        
        # Get model kwarg (is this the best place to set default values?):
#         self._baz = kwargs.get('baz', None) # TypeError: __init__() got an unexpected keyword argument 'baz'
        
        self._baz = baz
        
        super(TestField, self).__init__(*args, **kwargs)
    
    def formfield(self, **kwargs):
        
        # Set kwarg defaults:
        defaults = {
            'baz': _baz,
            'form_class': forms.TestField,
        }
        
        # Update kwargs with defaults:
        defaults.update(kwargs)
        
        return super(TestField, self).formfield(**defaults)

forms.py

from django.forms import fields
# from test import widgets

class TestField(fields.CharField):
    
    """
    Docstring...
    """
    
    description = 'Description...'
    
    def __init__(self, baz=None, *args, **kwargs):
        
        # Or this?
#         self.baz = kwargs.get('baz', None)
        
        # Call the widget:
#         self.widget = widgets.TestWidget(baz=baz, **kwargs)
        
        # Default kwargs:
        dwargs = {
            'required': True,
            'label': None,
            'initial': None,
            'help_text': None,
            'error_messages': None,
            'show_hidden_initial': False,
        }
        
        # Assign attribute values from kwargs to dwargs:
        for attr in dwargs:
            if attr in kwargs:
                dwargs[attr] = kwargs[attr]
        
        super(TestField, self).__init__(*args, **dwargs)
    
    def clean(self, value):
        
        # Do stuff with value here.
        
        pass

models.py

from django.db import models
from test.fields import TestField

class Test(models.Model):
    
    """
    Docstring...
    """
    
    description = 'Description...'
    
    foo = TestField(u'Foo field', baz='bar', max_length=100, help_text='Foo baz bar?')
    
    # I've hit a brick wall here:
    # __init__() got multiple values for keyword argument 'baz'
    # In line #12 above. :(

I have spent the last few days trying to get this to work (reading numerous sources, including docs) and nothing seems to be working.

Goal

Pass custom attribute to custom model field and eventually pass that off to a custom widget. :)

Problem

My model is complaining about baz attribute:

File "/.../test/models.py", line 12, in Test
foo = TestField(u'Foo field', baz='bar', max_length=100, help_text='Foo baz bar?')
TypeError: __init__() got multiple values for keyword argument 'baz'

Where have I gone wrong?

Notes

Original code found here.

I have used other code examples for inspiration and learning purposes, but the above code is closely related a project I am working on.

Discussion here