__repr__ vs repr

Question

这两种方法有区别吗？

例如,

from datetime import date
today = date(2012, 10, 13)
repr(today)
'datetime.date(2012, 10, 13);

today.__repr__()
'datetime.date(2012, 10, 13)'

他们似乎做了同样的事情,但为什么有人想要在常规报告中使用后者呢？

Answer 1

__repr__方法用于实现自定义结果repr().它被使用repr(),str()(如果__str__没有定义).你不应该__repr__明确地打电话.

不同之处在于repr()强制将字符串作为返回的类型,并且repr()__repr__在类对象上查找,而不是实例本身:

>>>> class C(object):
....   def __repr__(self):
....     return 1 # invalid non-string value
....
>>>> c = C()
>>>> c.__repr__() # works
1
>>>> repr(c) # enforces the rule
Traceback (most recent call last):
  File "<console>", line 1, in <module>
TypeError: __repr__ returned non-repr (type 'int')
>>>> c # calls repr() implicitly
Traceback (most recent call last):
  File "<console>", line 1, in <module>
TypeError: __repr__ returned non-repr (type 'int')
>>>> str(c)  # also uses __repr__
Traceback (most recent call last):
  File "<console>", line 1, in <module>
TypeError: __str__ returned non-str (type 'int')
>>>> c.__repr__ = lambda: "a"
>>>> c.__repr__() # lookup on instance
'a'
>>>> repr(c) # old method from the class
Traceback (most recent call last):
  File "<console>", line 1, in <module>
TypeError: __repr__ returned non-repr (type 'int')
>>>>