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Allow Fraction constructor to accept float and decimal instances directly. #52541

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mdickinson opened this issue Apr 2, 2010 · 7 comments
Closed

Allow Fraction constructor to accept float and decimal instances directly. #52541

mdickinson opened this issue Apr 2, 2010 · 7 comments
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@mdickinson
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stdlib Python modules in the Lib dir type-feature A feature request or enhancement

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@mdickinson
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BPO 8294
Nosy @rhettinger, @mdickinson
Files
  • fraction_from_float.patch
  • fraction_from_float2.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 = 'https://github.com/mdickinson'
closed_at = <Date 2010-04-03.11:40:56.050>
created_at = <Date 2010-04-02.20:42:41.715>
labels = ['type-feature', 'library']
title = 'Allow Fraction constructor to accept float and decimal instances directly.'
updated_at = <Date 2010-04-03.11:40:56.049>
user = 'https://github.com/mdickinson'

    bugs.python.org fields:

    activity = <Date 2010-04-03.11:40:56.049>
actor = 'mark.dickinson'
assignee = 'mark.dickinson'
closed = True
closed_date = <Date 2010-04-03.11:40:56.050>
closer = 'mark.dickinson'
components = ['Library (Lib)']
creation = <Date 2010-04-02.20:42:41.715>
creator = 'mark.dickinson'
dependencies = []
files = ['16738', '16740']
hgrepos = []
issue_num = 8294
keywords = ['patch']
message_count = 7.0
messages = ['102198', '102199', '102201', '102204', '102205', '102210', '102238']
nosy_count = 2.0
nosy_names = ['rhettinger', 'mark.dickinson']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue8294'
versions = ['Python 3.2']
    @mdickinson
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    Here's a patch that allows direct construction of a Fraction instance from a float or Decimal instance, performing an exact conversion in either case.

    >>> from fractions import Fraction
>>> from decimal import Decimal
>>> Fraction(1.1)
Fraction(2476979795053773, 2251799813685248)
>>> Fraction(Decimal('1.1'))
Fraction(11, 10)
>>> Fraction(Decimal(1.1))
Fraction(2476979795053773, 2251799813685248)

    @mdickinson mdickinson added stdlib Python modules in the Lib dir type-feature A feature request or enhancement labels Apr 2, 2010
    @mdickinson
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    (The patch is against trunk, btw.)

    @rhettinger
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    The patch looks like what I expected.

    In the docstring, it would be nice if we kept the line with the spec for decimal strings: [-+]?[0-9]+((/|.)[0-9]+)?

    @rhettinger rhettinger assigned mdickinson and unassigned rhettinger Apr 2, 2010
    @mdickinson
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    Unfortunately, that line is wrong (or at least incomplete), since decimals in exponential form are also accepted:

    >>> Fraction('2.3e4')
Fraction(23000, 1)

    I could try to reinstate a fixed version.

    Attaching a second version of the patch: same as the first, except for some doc tweaks. (Rewording, markup fixes.)

    @rhettinger
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    Being wrong is a good reason to eliminate that line from the docstring :-) So, I'm happy with the patch as-is.

    @mdickinson
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    Thanks, Raymond. Committed to trunk in r79629. Will forward port to py3k.

    @mdickinson
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    Merged to py3k in r79670.

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