Django 遇错: TypeError: 'NoneType' 对象没有属性 '__getitem__'

在使用 Django (对 Django 和 Python 都是新手) 搭建一个非常基本的联系人数据库时，使用 Admin 页面尝试在 Contributor 表中添加记录，但遇到了错误。Contributor 模型的代码如下所示：

class Contributor(models.Model):

first_name = models.CharField(max_length=20)
last_name = models.CharField(max_length=20)
organisation = models.ForeignKey('Organisation')
mode = models.CharField(max_length=10, blank=True)
email = models.CharField(max_length=30, blank=True)
landline = models.CharField(max_length=10, blank=True)

def __unicode__(self):
    print('%s %s' % (self.first_name, self.last_name))

错误信息如下：

Environment:

Request Method: POST
Request URL: http://127.0.0.1:8000/admin/ramapp/contributor/add/

Django Version: 1.5.5
Python Version: 2.7.5
Installed Applications:
('django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.sites',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'django.contrib.admin',
 'south',
 'ramapp')
Installed Middleware:
('django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware')


Traceback:
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  115.                         response = callback(request, *callback_args, **callback_kwargs)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/contrib/admin/options.py" in wrapper
  372.                 return self.admin_site.admin_view(view)(*args, **kwargs)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
  91.                     response = view_func(request, *args, **kwargs)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
  89.         response = view_func(request, *args, **kwargs)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/contrib/admin/sites.py" in inner
  202.             return view(request, *args, **kwargs)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapper
  25.             return bound_func(*args, **kwargs)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
  91.                     response = view_func(request, *args, **kwargs)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/utils/decorators.py" in bound_func
  21.                 return func(self, *args2, **kwargs2)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/db/transaction.py" in inner
  223.                 return func(*args, **kwargs)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/contrib/admin/options.py" in add_view
  1009.                 self.log_addition(request, new_object)
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/contrib/admin/options.py" in log_addition
  530.             action_flag     = ADDITION
File "/Users/lemon/.virtualenvs/ram/lib/python2.7/site-packages/django/contrib/admin/models.py" in log_action
  18.         e = self.model(None, None, user_id, content_type_id, smart_text(object_id), object_repr[:200], action_flag, change_message)

Exception Type: TypeError at /admin/ramapp/contributor/add/
Exception Value: 'NoneType' object has no attribute '__getitem__'

2. 解决方案：

根据错误提示，问题出在 Contributor 模型的 unicode 方法中。在该方法中，您使用了 print 语句来打印字符串，但实际上应该使用 return 语句来返回字符串。

改进后的 unicode 方法如下：

def __unicode__(self):
    return '%s %s' % (self.first_name, self.last_name)

这种修改将确保 unicode 方法返回字符串，从而避免 TypeError 异常。