printf("%lx") -> printf("%p") for pointers : win64 cares

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

BPO	400505
Nosy	@tim-one, @freddrake
Files	None: None

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields: ```python assignee = 'https://github.com/freddrake' closed_at = created_at = labels = [] title = 'printf("%lx") -> printf("%p") for pointers : win64 cares' updated_at = user = 'https://bugs.python.org/tmick' ``` bugs.python.org fields: ```python activity = actor = 'fdrake' assignee = 'fdrake' closed = True closed_date = None closer = None components = ['None'] creation = creator = 'tmick' dependencies = [] files = ['2436'] hgrepos = [] issue_num = 400505 keywords = ['patch'] message_count = 5.0 messages = ['32684', '32685', '32686', '32687', '32688'] nosy_count = 3.0 nosy_names = ['tim.peters', 'fdrake', 'tmick'] pr_nums = [] priority = 'normal' resolution = None stage = None status = 'closed' superseder = None type = None url = 'https://bugs.python.org/issue400505' versions = [] ```

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

[freddrake]

Checked in verbatim.

[tim-one]

Accepted & passed back to Trent. We *have* to check this one in, so David Ascher can eliminate all the tedious semaphore debug code you so tediously repaired \<wink>.

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

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[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

This is a revival submission. This got discussed (at least by Tim and I) and then it died.

Background:

The common technique for printing out a pointer has been to cast to a long and use the "%lx" printf modifier. This is incorrect on Win64 where casting to a long truncates the pointer. The "%p" formatter should be used instead.

before (with a debugging printf of my own):

>>> class spam: pass
...
>>> repr(spam)
real pointer value is 000003FFFFC58340   # my own printf in the class_repr fn
'<class __main__.spam at ffc58340>'
>>>

after:

>>> class spam: pass
...
>>> repr(spam)
'<class __main__.spam at 000003FFFFC58340>'
>>>

The problem as stated by Tim:

Unfortunately, the C committee refused to define what %p conversion "looks like" -- they explicitly allowed it to be implementation-defined. Older versions of Microsoft C even stuck a colon in the middle of the address (in the days of segment+offset addressing)!

The result is that the hex value of a pointer will maybe/maybe not have a 0x prepended to it.

[Tim answers some question of mine about this problem]

> I.e. does Python promise the repr output to look EXACTLY the way it does?

No.

> Will reasonable code out there break?

Probably, but not much. I'm sure much more code will break due to 1.6 dropping the trailing "L" on str(long), for example.

> ... > Given that %p is "implementation defined" do you see this patch > going in

I'd put it in, if I were Guido.

From here is Guido's call, I guess. So here is the patch (again).

Notes on the patch:

There are two main classes of changes:

• in the various repr() functions that print out pointers
• debugging printf's in the various thread_*.h files (these are why the patch is large)