str(list)

[Trevor Blackwell]

I wish that str of a list would call str on the elements, rather than
repr. Currently, list has only a repr function so it ends up calling
repr on its members.

The way to fix this would be to add a list_str in Objects/listobject.c
similar to list_repr.

An example:

class mytype:
def __init__(self, x):
self.x=x

def __str__(self):
return "mytype(%s)" % self.x

foo=mytype("foo")
bar=mytype("bar")

print foo # Prints mytype(foo)
print bar # Prints mytype(bar)
print [foo,bar] # Prints [<__main__.mytype instance at 0x81b21ac>,
# <__main__.mytype instance at 0x81b216c>]

 

[Donn Cave]

I wish that str of a list would call str on the elements, rather than
repr. Currently, list has only a repr function so it ends up calling
repr on its members.

The way to fix this would be to add a list_str in Objects/listobject.c
similar to list_repr.

An example:

class mytype:
def __init__(self, x):
self.x=x

def __str__(self):
return "mytype(%s)" % self.x

foo=mytype("foo")
bar=mytype("bar")

print foo # Prints mytype(foo)
print bar # Prints mytype(bar)
print [foo,bar] # Prints [<__main__.mytype instance at 0x81b21ac>,
# <__main__.mytype instance at 0x81b216c>]

You're not the first person to want this, but usually
it's because of the repr botch with floats. I think
in your case the answer could be for the classes to
define a more suitable __repr__ method.

I'm sure I'm forgetting one or more problems with the
solution you propose, but the first one that comes to
mind is that __str__ commonly returns values that would
be confusing in this context. Suppose you print strings -

>>> print ['A', 'B']

[A, B]

You may find this acceptable, but who would put up with this?

>>> print ['A, B', 'C']

[A, B, C]

Lists do not really have an appropriate str value - there
is no natural transformation of a list into a string value.
If there is, it's something like ['A', 'B'] -> 'AB'. The
brackets and commas are a notational thing that only makes
sense in repr.

Donn Cave, (e-mail address removed)