__repr__ vs repr

Question

Is there a difference between the two methods?

For example,

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

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

They seem to do the same thing, but why would someone want to use the latter over the regular repr?

Answer 1

__repr__ method is used to implement custom result for repr() . It is used by repr() , str() (if __str__ is not defined). You shouldn't call __repr__ explicitly.

The difference is that repr() enforces the string as the returned type and repr() looks up __repr__ on a class object, not an instance itself:

>>>> 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')
>>>>

Answer 2

It's the same thing

Think of repr() as containing the following code:

def repr(obj):
    return obj.__repr__()

All it does is call the object's __repr__() function. I'm not sure why anyone would need to call the object's __repr__() method explicitly. In fact, it's generally bad coding style to do so (it's confusing, and leads the programmer to ask questions like the one that you did just now).