Allow Fraction constructor to accept float and decimal instances directly.

[mdickinson]

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]

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]

(The patch is against trunk, btw.)

[rhettinger]

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]+)?

[mdickinson]

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]

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

[mdickinson]

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

[mdickinson]

Merged to py3k in r79670.