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From: Peter Otten <__peter__@web.de>
Subject: Re: New internal string format in 3.3
Date: Sun, 19 Aug 2012 11:37:09 +0200
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Steven D'Aprano wrote:

> On Sun, 19 Aug 2012 09:43:13 +0200, Peter Otten wrote:
> 
>> Steven D'Aprano wrote:
> 
>>> I don't know where people are getting this myth that PEP 393 uses
>>> Latin-1 internally, it does not. Read the PEP, it explicitly states
>>> that 1-byte formats are only used for ASCII strings.
>> 
>> From
>> 
>> Python 3.3.0a4+ (default:10a8ad665749, Jun  9 2012, 08:57:51) [GCC
>> 4.6.1] on linux
>> Type "help", "copyright", "credits" or "license" for more information.
>>>>> import sys
>>>>> [sys.getsizeof("é"*i) for i in range(10)]
>> [49, 74, 75, 76, 77, 78, 79, 80, 81, 82]
> 
> Interesting. Say, I don't suppose you're using a 64-bit build? Because
> that would explain why your sizes are so larger than mine:
> 
> py> [sys.getsizeof("é"*i) for i in range(10)]
> [25, 38, 39, 40, 41, 42, 43, 44, 45, 46]
> 
> 
> py> [sys.getsizeof("€"*i) for i in range(10)]
> [25, 40, 42, 44, 46, 48, 50, 52, 54, 56]

Yes, I am using a 64-bit build. I thought that

>> (2) Latin1 strings have a constant overhead of 24 bytes (on a 64bit 
>> system) over ASCII-only.

would convey that. The corresponding data structure 

typedef struct {
  PyASCIIObject _base;
  Py_ssize_t utf8_length;
  char *utf8;
  Py_ssize_t wstr_length;
} PyCompactUnicodeObject;

makes for 12 extra bytes on 32 bit, and both Py_ssize_t and pointers double 
in size (from 4 to 8 bytes) on 64 bit. I'm sure you can do the maths for the 
embedded PyASCIIObject yourself.