[Python-Dev] Access to bits for a PyLongObject

Eric V. Smith eric+python-dev at trueblade.com
Wed Mar 7 14:03:29 CET 2007

Martin v. Löwis wrote:
> Ah, I had missed the point that it's just binary formatting that
> you are concerned with (and then I missed that binary is "base 2",
> rather than "sequence of bits")

Apologies for not being clear.  It's easy to forget that others don't 
share the context of something you've been immersed in.

>> Having written all of this, I'm now thinking that Nick's suggestion of 
>> _PyLong_AsByteArray might be the way to go.  I would use that for all of
>> my formatting for longs.  
> How would you do negative numbers, then? AsByteArray gives you two's
> complement.


>> But I'd like PEP 3101 to be as efficient as possible,
>> because once it's available I'll replace all of the '%' string
>> formatting in my code with it.  
> That is fine. However, don't trade efficiency for maintainability.
> Keep encapsulation of types, this is what OO is for. Modularize
> along with type boundaries. If that loses efficiency, come up with
> interfaces that still modularize in that way but are efficient.
> Don't "hack" to achieve performance. (Any other way I can formulate
> the same objective :-?)

Point taken.  I currently have it using PyLong internals, just to get 
our tests to pass and so Pat can work on his part.  As we still want to 
be a standalone module for a while, I'm going to modify the code to use 
AsByteArray and Sign to do the binary formatting only.

When/if we integrate this into 3.0 (and 2.6, I hope), I'll look at 
adding __format__ to long, and possibly the other built in types.  To do 
so we'll need to factor some code out to a library, because it doesn't 
make sense for all the built-in types to understand how to parse and 
operate on the format specifiers (the 
[[fill]align][sign][width][.precision][type] stuff).

Thanks for your comments!


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