Is this a bug?

[Robert Kern]

Michael Sparks wrote:
> Hi,
> 
> 
> I've hit a corner case that I can explain to myself *why* it happens, both
> under python 2.3 and python 2.4, but the following inconsistency makes me
> wonder if I should log it as a bug:
> 
> First the behaviour that isn't unexpected:
> 
> 
>>>>a=["hello"]
>>>>a = a + "world"
> 
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> TypeError: can only concatenate list (not "str") to list
> 
> 
> Which is pretty what I'd expect.
> 
> However if we do this just slightly differently:
> 
> 
>>>>a = ["hello"]
>>>>a += "world"
>>>>a
> 
> ['hello', 'w', 'o', 'r', 'l', 'd']
> 
> We get completely different behaviour. This strikes me as a bug - should I
> log it as one, or is there a good reason for this behaviour?

It's consistent with using a.extend("world") which is what the += is 
sugar for.

In [1]:a = ['hello']

In [2]:a.extend("world")

In [3]:a
Out[3]:['hello', 'w', 'o', 'r', 'l', 'd']

It's a *good* thing that .extend() takes any iterable without explicit 
conversion to a list. I think that it's just a minor annoyance that the 
behavior passes on to +=.

-- 
Robert Kern
rkern at ucsd.edu

"In the fields of hell where the grass grows high
  Are the graves of dreams allowed to die."
   -- Richard Harter