[Python-Dev] list += string?? (original) (raw)

David Abrahams dave at boost-consulting.com
Thu Aug 26 16:58:26 CEST 2004

Tim Peters <tim.peters at gmail.com> writes:

[David Abrahams]

I just discovered the following behavior:

C:\Documents and Settings\dave>python Python 2.3 (#46, Aug 25 2003, 18:37:29) [MSC v.1200 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> prefix = ['foo', 'bar', 'baz'] >>> prefix += 'bomb' # meant to write prefix += [ 'bomb' ] >>> prefix ['foo', 'bar', 'baz', 'b', 'o', 'm', 'b'] >>> Is it new and/or intentional? I would have expected an error from the +=. I was very surprised when my error "passed silently". It was new when the iterator protocol was introduced. It wasn't explicitly intended that you get surprises for strings specifically, but it was explicitly intended that list += whatever work like list.extend(whatever) and that whatever can be any iterable object.

I figured as much.

Since strings are iterable objects, it's no more or less surprising than that 'for ch in "bomb"' works too .

I want my ,= operator!

-- Dave Abrahams Boost Consulting http://www.boost-consulting.com

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