现在，让我们进入Python的交互式shell，玩转这些Django提供给你的API。 使用如下命令来调用Python shell：

$ python manage.py shell

我们使用上述命令而不是简单地键入“python”进入python环境，是因为manage.py 设置了DJANGO_SETTINGS_MODULE 环境变量，该变环境变量告诉Django导入mysite/settings.py文件的路径。

绕开 manage.py

如果你不想使用manage.py，也没问题。只要设置 环境变量为 mysite.settings，启动一个普通的Python shell，然后建立Django：

>>> import django>>> django.setup()

如果以上命令引发了一个，可能是你使用了一个和本教程不匹配的Django版本。 你可能需要换一个老一点的教程或者换一个新一点的Django版本。

你必须在与manage.py相同的目录下运行python，或确保你的目录在Python 的路径中，这样import mysite才可以工作。

所有这些信息，请参见。

一旦你进入这个shell，请探索这些：

>>> from polls.models import Question, Choice # Import the model classes we just wrote. # No questions are in the system yet. >>> Question.objects.all() [] # Create a new Question. # Support for time zones is enabled in the default settings file, so # Django expects a datetime with tzinfo for pub_date. Use timezone.now() # instead of datetime.datetime.now() and it will do the right thing. >>> from django.utils import timezone >>> q = Question(question_text="What's new?", pub_date=timezone.now()) # Save the object into the database. You have to call save() explicitly. >>> q.save() # Now it has an ID. Note that this might say "1L" instead of "1", depending # on which database you're using. That's no biggie; it just means your # database backend prefers to return integers as Python long integer # objects. >>> q.id 1 # Access model field values via Python attributes. >>> q.question_text "What's new?" >>> q.pub_date datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=
      
       ) # Change values by changing the attributes, then calling save(). >>> q.question_text = "What's up?" >>> q.save() # objects.all() displays all the questions in the database. >>> Question.objects.all() [
       
        ]
       
      

先等一下。<Question: Question object>对于这个对象是一个完全没有意义的表示。 让我们来修复这个问题，编辑Question模型（在polls/models.py文件中）并添加一个方法给Question和Choice：

polls/models.py

from django.db import modelsclass Question(models.Model): # ... def __str__(self): # __unicode__ on Python 2 return self.question_text class Choice(models.Model): # ... def __str__(self): # __unicode__ on Python 2 return self.choice_text

给你的模型添加方法很重要，不仅会使你自己在使用交互式命令行时看得更加方便，而且会在Django自动生成的管理界面中使用对象的这种表示。

__str__ 还是 __unicode__?

对于Python 3来说，这很简单，只需使用。

对于Python 2来说，你应该定义方法并返回unicode 值。Django 模型具有一个默认的 方法，它会调用并将结果转换为UTF-8 字节字符串。这意味着unicode(p)将返回一个Unicode 字符串，而str(p)将返回一个字节字符串，其字符以UTF-8编码。Python 的行为则相反：对象的__unicode__方法调用 __str__方法并将结果理解为ASCII 字节字符串。这个不同点可能会产生困惑。

如果以上这些令你费解的话，那就使用Python 3吧。

请注意这些都是普通的Python方法。 让我们演示一下如何添加一个自定义的方法：

polls/models.py

import datetimefrom django.db import models from django.utils import timezone class Question(models.Model): # ... def was_published_recently(self): return self.pub_date >= timezone.now() - datetime.timedelta(days=1)

注意import datetime 和from django.utils import timezone分别引用Python 的标准 模块和Django中时区相关的工具。如果你不了解Python中时区的处理方法，你可以在 中了解更多的知识。

保存这些改动，然后通过python manage.py shell再次打开一个新的Python 交互式shell：

>>> from polls.models import Question, Choice # Make sure our __str__() addition worked. >>> Question.objects.all() [
      
       ] # Django provides a rich database lookup API that's entirely driven by # keyword arguments. >>> Question.objects.filter(id=1) [
       
        ] >>> Question.objects.filter(question_text__startswith='What') [
        
         ] # Get the question that was published this year. >>> from django.utils import timezone >>> current_year = timezone.now().year >>> Question.objects.get(pub_date__year=current_year) 
         
           # Request an ID that doesn't exist, this will raise an exception. >>> Question.objects.get(id=2) Traceback (most recent call last): ... DoesNotExist: Question matching query does not exist. # Lookup by a primary key is the most common case, so Django provides a # shortcut for primary-key exact lookups. # The following is identical to Question.objects.get(id=1). >>> Question.objects.get(pk=1) 
          
            # Make sure our custom method worked. >>> q = Question.objects.get(pk=1) >>> q.was_published_recently() True # Give the Question a couple of Choices. The create call constructs a new # Choice object, does the INSERT statement, adds the choice to the set # of available choices and returns the new Choice object. Django creates # a set to hold the "other side" of a ForeignKey relation # (e.g. a question's choice) which can be accessed via the API. >>> q = Question.objects.get(pk=1) # Display any choices from the related object set -- none so far. >>> q.choice_set.all() [] # Create three choices. >>> q.choice_set.create(choice_text='Not much', votes=0) 
           
             >>> q.choice_set.create(choice_text='The sky', votes=0) 
            
              >>> c = q.choice_set.create(choice_text='Just hacking again', votes=0) # Choice objects have API access to their related Question objects. >>> c.question 
             
               # And vice versa: Question objects get access to Choice objects. >>> q.choice_set.all() [
              
               , 
               
                , 
                
                 ] >>> q.choice_set.count() 3 # The API automatically follows relationships as far as you need. # Use double underscores to separate relationships. # This works as many levels deep as you want; there's no limit. # Find all Choices for any question whose pub_date is in this year # (reusing the 'current_year' variable we created above). >>> Choice.objects.filter(question__pub_date__year=current_year) [
                 
                  , 
                  
                   , 
                   
                    ] # Let's delete one of the choices. Use delete() for that. >>> c = q.choice_set