Description

stevendaprano

opened on Mar 26, 2022

Issue body actions

BPO	47134
Nosy	@stevendaprano, @eryksun

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

Show more details

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2022-03-26.22:10:10.212>
labels = ['3.7', '3.8', '3.9', '3.10', '3.11', 'type-feature', 'docs']
title = 'Document the meaning of the number in OverflowError'
updated_at = <Date 2022-03-26.22:46:01.129>
user = 'https://github.com/stevendaprano'

bugs.python.org fields:

activity = <Date 2022-03-26.22:46:01.129>
actor = 'eryksun'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2022-03-26.22:10:10.212>
creator = 'steven.daprano'
dependencies = []
files = []
hgrepos = []
issue_num = 47134
keywords = []
message_count = 2.0
messages = ['416093', '416096']
nosy_count = 3.0
nosy_names = ['steven.daprano', 'docs@python', 'eryksun']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue47134'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']

Activity

1. stevendaprano commented on Mar 26, 2022

   

   stevendaprano

   on Mar 26, 2022

   MemberAuthor

   More actions

   OverflowError sometimes (but not always) includes some sort of numeric code:

   >>> 1e+300 ** 2
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   OverflowError: (34, 'Numerical result out of range')

   but the meaning of the 34 is not documented:

   https://docs.python.org/3/library/exceptions.html#OverflowError

   help(OverflowError) is no more insightful, saying only:

       __init__(self, /, *args, **kwargs)
           Initialize self.  See help(type(self)) for accurate signature.

   Other OverflowError exceptions do not include the numeric code:

   >>> math.exp(10000)
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   OverflowError: math range error

   Is it an error code from C? Something to do with the number of digits of precision? An easter-egg to do with The Count Of Monte Cristo?

   Reacted by Václav Brožík
2. stevendaprano

   added

   3.7 (EOL)end of lifeend of life

   3.8 (EOL)end of lifeend of life

   3.9 (EOL)end of lifeend of life

   3.10 (EOL)end of lifeend of life

   3.11only security fixesonly security fixes

   on Mar 26, 2022
3. stevendaprano

   assigned

   docspython

   on Mar 26, 2022
4. stevendaprano

   added

   3.9 (EOL)end of lifeend of life

   docsDocumentation in the Doc dirDocumentation in the Doc dir

   3.10 (EOL)end of lifeend of life

   type-featureA feature request or enhancementA feature request or enhancement

   3.11only security fixesonly security fixes

   on Mar 26, 2022
5. stevendaprano

   assigned

   docspython

   on Mar 26, 2022
6. stevendaprano

   added

   docsDocumentation in the Doc dirDocumentation in the Doc dir

   type-featureA feature request or enhancementA feature request or enhancement

   on Mar 26, 2022
7. eryksun commented on Mar 26, 2022

   

   eryksun

   on Mar 26, 2022

   Contributor

   More actions

   The error code for 1e+300 ** 2 is ERANGE, from calling libm pow(). Since pow() returns a double, there's no way to indicate an error in the return value. Instead, C errno is set to 0 beforehand and checked for a non-zero error value after the call. If the error code isn't ERANGE, then float.pow() raises ValueError instead of OverflowError. Here's the relevant snippet from float_pow() in Objects/floatobject.c:

   /* Now iv and iw are finite, iw is nonzero, and iv is
    * positive and not equal to 1.0.  We finally allow
    * the platform pow to step in and do the rest.
    */
   errno = 0;
   ix = pow(iv, iw);
   _Py_ADJUST_ERANGE1(ix);
   if (negate_result)
       ix = -ix;
   

       if (errno != 0) {
           /* We don't expect any errno value other than ERANGE, but
            * the range of libm bugs appears unbounded.
            */
           PyErr_SetFromErrno(errno == ERANGE ? PyExc_OverflowError :
                                PyExc_ValueError);
           return NULL;
       }
       return PyFloat_FromDouble(ix);

   Here's a direct example using ctypes:

       import ctypes
       import errno
   
       libm = ctypes.CDLL('libm.so.6', use_errno=True)
       libm.pow.argtypes = (ctypes.c_double, ctypes.c_double)
       libm.pow.restype = ctypes.c_double

       >>> errno.ERANGE
       34
       >>> ctypes.set_errno(0)
       0
       >>> libm.pow(1e300, 2)
       inf
       >>> ctypes.get_errno() == errno.ERANGE
       True

   Reacted by Stanley
8. ezio-melotti

   transferred this issue fromon Apr 10, 2022
9. slateny commented on Sep 9, 2022

   

   slateny

   on Sep 9, 2022

   Contributor

   More actions

   For improvements, maybe the errno page can directly list the constant equivalents, and then the page could be referenced in the exceptions page?

Issue actions