sys.maxfloat patch

[tiran]

BPO	1534
Nosy	@gvanrossum, @mdickinson, @tiran
Files	trunk_maxfloat.patch

^{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:

assignee = None
closed_at = <Date 2007-12-01.11:24:11.400>
created_at = <Date 2007-12-01.01:22:16.602>
labels = ['interpreter-core']
title = 'sys.maxfloat patch'
updated_at = <Date 2008-01-06.22:29:44.719>
user = 'https://github.com/tiran'

bugs.python.org fields:

activity = <Date 2008-01-06.22:29:44.719>
actor = 'admin'
assignee = 'none'
closed = True
closed_date = <Date 2007-12-01.11:24:11.400>
closer = 'christian.heimes'
components = ['Interpreter Core']
creation = <Date 2007-12-01.01:22:16.602>
creator = 'christian.heimes'
dependencies = []
files = ['8840']
hgrepos = []
issue_num = 1534
keywords = ['patch']
message_count = 9.0
messages = ['58037', '58038', '58041', '58051', '58053', '58054', '58055', '58062', '58075']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'mark.dickinson', 'christian.heimes']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1534'
versions = ['Python 2.6', 'Python 3.0']

[tiran]

Currently Python has no information about the maximum and minimum value
of a float. The patch adds a dict with all important information to sys:

>>> pprint.pprint(sys.maxfloat)
{'dig': 15,
 'epsilon': 2.2204460492503131e-16,
 'mant_dig': 53,
 'max': 1.7976931348623157e+308,
 'max_10_exp': 308,
 'max_exp': 1024,
 'min': 2.2250738585072014e-308,
 'min_10_exp': -307,
 'min_exp': -1021,
 'radix': 2,
 'rounds': 1}

The patch compiles on Linux and Windows.

[gvanrossum]

I'd suggest giving it a different name, maybe float_info. sys.maxfloat
suggests the value is a float, like sys.maxint and sys.maxunicode.

[tiran]

Applied in r59254.

I've moved the code to floatobject.c/h and added PyFloat_GetMax() and
PyFloat_GetMin(), too. The intobject.c file has a similar function.

[mdickinson]

A (probably stupid) question: what's supposed to happen on platforms that
don't define things like DBL_MAX_10_EXP, which isn't part of ANSI C89? Or
are there no such platforms?

[tiran]

I've checked all major platforms before committing the patch. They all
have a float.h with the information available. Do you know of a platform
where this information isn't available? I could add a lot of #ifdef but
I don't feel like bloating the code unless it is necessary.

[mdickinson]

No, I don't know of any platforms that don't define these constants.

[mdickinson]

And it looks as though DBL_MAX_10_EXP *is* part of ANSI C anyway... I
shouldn't have assumed that just because it's not in Kernighan and Ritchie
(2nd edition) it doesn't exist... Apologies.

[tiran]

Thanks for checking it out for me! Do you have a reliable online source
for the ANSI C89 standard? I'm usually using the GNU C Library docs but
the site doesn't list what's available in C89.

[mdickinson]

The site that persuaded me about DBL_MAX_10_EXP was

http://www.schweikhardt.net/identifiers.html

Googling 'C89 draft' also turns up some potentially useful stuff.