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repr() and str() are identical for floats in 3.5 #70429

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andersrundgrennetgmailcom mannequin opened this issue Jan 30, 2016 · 6 comments
Closed

repr() and str() are identical for floats in 3.5 #70429

andersrundgrennetgmailcom mannequin opened this issue Jan 30, 2016 · 6 comments
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@andersrundgrennetgmailcom
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Mannequin

BPO 26241
Nosy @mdickinson, @ericvsmith, @vadmium, @eryksun

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 2016-01-30.10:31:52.952>
created_at = <Date 2016-01-30.09:22:04.073>
labels = ['invalid', 'docs']
title = 'repr() and str() are identical for floats in 3.5'
updated_at = <Date 2016-01-30.22:33:57.538>
user = 'https://bugs.python.org/andersrundgrennetgmailcom'

bugs.python.org fields:

activity = <Date 2016-01-30.22:33:57.538>
actor = 'eric.smith'
assignee = 'docs@python'
closed = True
closed_date = <Date 2016-01-30.10:31:52.952>
closer = 'mark.dickinson'
components = ['Documentation']
creation = <Date 2016-01-30.09:22:04.073>
creator = 'anders.rundgren.net@gmail.com'
dependencies = []
files = []
hgrepos = []
issue_num = 26241
keywords = []
message_count = 6.0
messages = ['259244', '259246', '259247', '259248', '259249', '259256']
nosy_count = 7.0
nosy_names = ['mark.dickinson', 'eric.smith', 'SilentGhost', 'docs@python', 'martin.panter', 'eryksun', 'anders.rundgren.net@gmail.com']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue26241'
versions = ['Python 3.5']
@andersrundgrennetgmailcom
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Mannequin Author

According to the documentation repr() and str() are different when it comes to number formatting. A test with a 100 million random and selected IEEE 64-bit values returned no differences

@andersrundgrennetgmailcom andersrundgrennetgmailcom mannequin added the interpreter-core (Objects, Python, Grammar, and Parser dirs) label Jan 30, 2016
@SilentGhost
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SilentGhost mannequin commented Jan 30, 2016

Would you mind linking to the relevant part of documentation?

@vadmium
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vadmium commented Jan 30, 2016

This discrepancy was supposed to be eliminated in 3.2; see bpo-9337. So assuming you are looking at the right version, it is the documentation that is at fault.

@vadmium vadmium added docs Documentation in the Doc dir and removed interpreter-core (Objects, Python, Grammar, and Parser dirs) labels Jan 30, 2016
@eryksun
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eryksun commented Jan 30, 2016

A test with a 100 million random and selected IEEE 64-bit values
returned no differences

The float type's tp_str and tp_repr both call float_repr in Objects/floatobject.c. See the 3.5.1 PyFloat_Type definition 1.

Perhaps you were reading something in reference to Python 2, which has separate float_str and float_repr functions. See the 2.7.11 PyFloat_Type definition 2 and the header file where PyFloat_STR_PRECISION is defined to be 12 digits 3.

@mdickinson
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Closing: as Martin pointed out, the behaviour is intentional, and without a reference to a particular part of the documentation this issue isn't useful. (Anders: if you find a part of the 3.5 documentation that does state that str and repr are different for floats, please feel free to re-open and link to that section of the documentation so that it can be fixed.)

@andersrundgrennetgmailcom
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Apparently the docs have changed since 2.7:
https://docs.python.org/3.5/tutorial/floatingpoint.html

However, the documentation still "sort of" mentions repr() as the most accurate form which isn't entirely correct since it nowadays is identical to str() for floats.

No big deal, I just thought I was doing something wrong :-)

related: http://bugs.python.org/issue26229

@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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@mdickinson @eryksun @vadmium