On 4/5/2012 13:44, Michael Hrivnak wrote: > This is not a gotcha, and it's not surprising. As John described, > you're assigning a new value to an index of a tuple, which tuples > don't support.
Um, at least for me personally, yes, it is surprising, and yes, it is a gotcha. This goes back to what languages you're used to. I come from a strong C++ background. In C++, something like mytuple[0] += [3] would wind up calling 'operator+=' on the list, that += would mutate the list, and then the expression would be done. The C++ approach doesn't really work with Python because more stuff is immutable, and Python's behavior is arguably the least-bad solution, but it WAS definitely surprising for me (and others!) when I learned about Python's behavior. In particular, the translation of 'a+=b' to 'temp = a + b; a = temp' is *not* a very natural one to me. Evan > > Michael > > On Thu, Apr 5, 2012 at 10:15 AM, John Posner <jjpos...@optimum.net> wrote: >> On 4/4/2012 7:32 PM, Chris Angelico wrote: >>> Don't know if it's what's meant on that page by the +=perator, >> >> Yes, it is. >> >>>> a=1],) >>>> a[0].append(2) # This is fine >> >> [In the following, I use the term "name" rather loosely.] >> >> The append() method attempts to modify the object whose name is "a[0]". >> That object is a LIST, so the attempt succeeds. >> >>>> a[0]+=] # This is not. >> >> The assignment attempts to modify the object whose name is "a". That >> object is a TUPLE, so the attempt fails. This might be a surprise, but >> I'm not sure it deserves to be called a wart. >> >> Note the similarity to: >> >> temp =[0] + [3] # succeeds >> a[0] =emp # fails >> >> -John >> >> >> >> >> -- >> http://mail.python.org/mailman/listinfo/python-list >
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