[Python-Dev] PEP 393 review (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Fri Aug 26 12:29:29 CEST 2011

But strings are allocated via PyObjectMalloc(), i.e. the custom arena-based allocator -- isn't its overhead (for small objects) less than 2 pointers per block?

Ah, right, I missed that. Indeed, those have no header, and the only overhead is the padding to a multiple of 8.

That shifts the picture; I hope the table below is correct, assuming ASCII strings. 3.2: 7 pointers (adds 4 bytes padding on 32-bit systems) 393: 10 pointers

string | 32-bit pointer | 32-bit pointer | 64-bit pointer size | 16-bit wchar_t | 32-bit wchar_t | 32-bit wchar_t | 3.2 | 393 | 3.2 | 393 | 3.2 | 393 |

1 | 40 | 48 | 40 | 48 | 64 | 88 | 2 | 40 | 48 | 48 | 48 | 72 | 88 | 3 | 40 | 48 | 48 | 48 | 72 | 88 | 4 | 48 | 48 | 56 | 48 | 80 | 88 | 5 | 48 | 48 | 56 | 48 | 80 | 88 | 6 | 48 | 48 | 64 | 48 | 88 | 88 | 7 | 48 | 48 | 64 | 48 | 88 | 88 | 8 | 56 | 56 | 72 | 56 | 96 | 86 |

So 1-byte strings increase in size; very short strings increase on 16-bit-wchar_t systems and 64-bit systems. Short strings keep there size, and long strings save.

Regards, Martin

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