[Python-3000] struni and the Apple four-character-codes (original) (raw)

Guido van Rossum guido at python.org
Wed Jul 25 07:44:17 CEST 2007

Make them bytes literals (some code already does this), and convert them to integers when they're needed to be used as hash keys. (Does this happen a lot? I haven't seen it yet.)

I would endorse an API to create an int from a bytes array (or arbitrary length) and vice versa -- that would be a useful way to marshal long integers, too. There's probably already a C API to do something like that.

--Guido

On 7/24/07, Talin <talin at acm.org> wrote:

Jeffrey Yasskin wrote: > I'm looking through a couple of the OS X tests and have run into the > question of what to do with four-character codes. (For those of you > who are unfamiliar with these, Apple, around the dawn of time, decided > that C constants like 'TEXT' (yes, those are single quotes) would > compile to the uint32t 0x54455854 (or maybe the other-endian version > of that) so they could use these as cheap-but-readable type > identifiers.) In Python 2, these are represented as 'str' instances, > which PyMacGetOSType() in Python/mactoolboxglue.c converts to the > native int format. For Python 3, right now they're str8's, but str8 is > theoretically supposed to go away. Because they're binary constants > displayed as ASCII, not unicode text, I initially thought that 'bytes' > was the appropriate type. Unfortunately, bytes is mutable, and I think > it makes sense to hash these constants (and some code in aepack.py > does). > > So, I'm stuck and wanted to ask the list for input. I see 5 options: > 1) Make these str instances so they're immutable and just rely on > convention and runtime errors to keep them in ascii. > 2) Make them bytes, and cast them to something else when you want to > make them keys in a dict. > 3) Keep them str8 and give up on getting rid of it. > 4) Make bytes immutable, add a 'buffer' type which acts like the > current bytes type, and make these codes instances of bytes. [probably > impossible this late in the game] > 5) Make a new hashable class for these codes which converts them to > and from ints and bytes and becomes the general argument type for the > apple platform interface. [Cleanest, but lots of work that I'm not > volunteering to do] > > Thoughts? > Jeffrey

Yeah. I like the idea of converting them to integers, but I don't think you need a special hash table class for that. Instead, create a wrapper class for the four character codes: TextId = FourCharId("TEXT") i = int(TextId) # Integer value s = str(TextId) # String representation somemap[TextId] = "Some Text" # Can use as dict key The wrapper class is an immutable class that handles conversion to integer form in the constructor, hashing, and has a str and repr method that produces the original input string. Then you can use that as a key to a regular dict. -- Talin

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-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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