django的model中 def __unicode__(self): 与 def __str__(self): 做什么用的
在Django中，Python3只能用__str__方法，Python2就使用__unicode__方法。因为更安全一些。
这个__str__的作用是美化打印出来的结果，使人类更方便查看。
看下面例子，如果没有__str__方法，打印的结果是<__main__.Test object at 0x0000022D6D1387B8>格式，
有了__str__方法后，打印时会按照__str__定义的格式来打印，打印结果为Name:xiaoming
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class Test:
def __init__(self, name, job):
self.name = name
self.job = job
def __str__(self):
return 'Name:' + self.name
instance = Test('xiaoming', 'Teacher')
print(instance)
__str__()
Model.__str__()
The __str__() method is called whenever you call str() on an object. Django uses str(obj) in a number of places. Most notably, to display an object in the Django admin site and as the value inserted into a template when it displays an object. Thus, you should always return a nice, human-readable representation of the model from the __str__() method.
For example:
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from django.db import models
class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
def __str__(self):
return '%s %s' % (self.first_name, self.last_name)
__str__() and __unicode__() methods
In Python 2, the object model specifies __str__() and __unicode__()_ methods. If these methods exist, they must return str (bytes) and unicode (text) respectively.
The print statement and the str built-in call __str__() to determine the human-readable representation of an object. The unicode built-in calls __unicode__()_ if it exists, and otherwise falls back to __str__() and decodes the result with the system encoding. Conversely, the Model base class automatically derives __str__() from __unicode__()_ by encoding to UTF-8.
In Python 3, there’s simply __str__(), which must return str (text).
(It is also possible to define __bytes__(), but Django applications have little use for that method, because they hardly ever deal with bytes.)
Django provides a simple way to define __str__() and __unicode__()_ methods that work on Python 2 and 3: you must define a __str__() method returning text and to apply the python_2_unicode_compatible() decorator.
On Python 3, the decorator is a no-op. On Python 2, it defines appropriate __unicode__()_ and __str__() methods (replacing the original __str__() method in the process). Here’s an example:
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from __future__ import unicode_literals
from django.utils.encoding import python_2_unicode_compatible
@python_2_unicode_compatible
class MyClass(object):
def __str__(self):
return "Instance of my class"
This technique is the best match for Django’s porting philosophy.
For forwards compatibility, this decorator is available as of Django 1.4.2.
Finally, note that __repr__() must return a str on all versions of Python.