Python unicode error

Question

Can someone explain me why in example below, print a raises exception, while a.__str__() doesn't?

>>> class A:
... def __init__(self):
... self.t1 = "čakovec".decode("utf-8")
... self.t2 = "tg"
... def __str__(self):
... return self.t1 + self.t2
... 
>>> a = A()
>>> print a
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\u010d' in position 0: ordinal not in range(128)
>>> a.__str__()
u'\u010dakovectg'
>>> print a.__str__()
čakovectg

Answer 1

In Python 2 str must return an ASCII string. When you call __str__ directly you're skipping the step of Python converting the output of __str__ to an ASCII string (you could in fact return whatever you want from __str__, but you shouldn't). __str__ should not return a unicode object, it should return a str object.

Here's something you can do instead:

In [29]: class A(object):
 ...: def __init__(self):
 ...: self.t1 = u"c∃".encode('utf8')
 ...: def __str__(self):
 ...: return self.t1
 ...: 
In [30]: a = A()
In [31]: print a
c∃
In [32]: str(a)
Out[32]: 'c\xe2\x88\x83'
In [33]: a.__str__()
Out[33]: 'c\xe2\x88\x83'