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[Python-Dev] Usage of += on strings in loops in stdlib

Larry Hastings larry at hastings.org
Wed Feb 13 09:52:18 CET 2013 
On 02/12/2013 05:25 PM, Christian Tismer wrote:
> Ropes have been implemented by Carl-Friedrich Bolz in 2007 as I remember.
> No idea what the impact was, if any at all.
> Would ropes be an answer (and a simple way to cope with string mutation
> patterns) as an alternative implementation, and therefore still justify
> the usage of that pattern?

I've always hated the "".join(array) idiom for "fast" string 
concatenation--it's ugly and it flies in the face of TOOWTDI.  I think 
everyone should use "x = a + b + c + d" for string concatenation, and we 
should just make that fast.

In 2006 I proposed "lazy string concatenation", a sort of rope that hid 
the details inside the string object.  If a and b are strings, a+b 
returned a string object that internally lazily contained references to 
a and b, and only computed its value if you asked for it.  Here's the 
Unicode version:

    http://bugs.python.org/issue1629305

Why didn't it get accepted?  I lumped in lazy slicing, a bad move as it 
was more controversial.  That and the possibility that macros like 
PyUnicode_AS_UNICODE could now possibly fail, which would have meant 
checking 400+ call sites to ensure they handle the possibility of 
failure.  This latter work has already happened with the new efficient 
Unicode representation patch.

I keep thinking it's time to revive the lazy string concatenation patch.


//arry/
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