printing list, is this a bug?

[William Chang]

Is the different behavior between __repr__ and __str__ intentional
when it comes to printing lists? Basically I want to print out a list
with elements of my own class, but when I overwrite __str__, __str__
doesn't get called but if I overwrite __repr__, __repr__ will get
called. Is this a bug?

For example:

>>class StrElement(object):

.... def __str__(self):
.... return "String Element"
....

>>a = [StrElement(), StrElement()]
print a

[<__main__.StrElement object at 0xb7dc05cc>, <__main__.StrElement
object at 0xb7dc048c>]

>>print StrElement()

String Element

But if overwrite __repr__:

>>class ReprElement(object):

.... def __repr__(self):
.... return "Repr Element"
....

>>b = [ReprElement(), ReprElement()]
print b

[Repr Element, Repr Element]

>>print ReprElement()

Repr Element

[Robert Kern]

William Chang wrote:

Is the different behavior between __repr__ and __str__ intentional
when it comes to printing lists? Basically I want to print out a list
with elements of my own class, but when I overwrite __str__, __str__
doesn't get called but if I overwrite __repr__, __repr__ will get
called. Is this a bug?

No, it's deliberate design. The string representation of a list object, either
list.__str__() or list.__repr__(), uses the __repr__() of its contained objects.

--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco

[William Chang]

oh okay. thanks.

[Dan Bishop]

On May 25, 3:55 pm, William Chang <[e-mail]:

Is the different behavior between __repr__ and __str__ intentional
when it comes to printing lists? Basically I want to print out a list
with elements of my own class, but when I overwrite __str__, __str__
doesn't get called but if I overwrite __repr__, __repr__ will get
called. Is this a bug?
...

As has been mentioned, this was a deliberate design decision. Partly
to make things like str(['a', 'b, c']) less confusing.