Skip to content

bpo-44258: support PEP 515 for Fraction's initialization from string #26422

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 11 commits into from
Jun 7, 2021
Merged

bpo-44258: support PEP 515 for Fraction's initialization from string #26422

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
11 commits
Select commit Hold shift + click to select a range
aa8249a
bpo-44258: support PEP 515 for Fraction's initialization from string
skirpichev May 28, 2021
8c96355
regexps's version
skirpichev May 28, 2021
8c62c64
Merge branch 'main' into fix-44258
skirpichev May 29, 2021
38b16a9
A different regexps version, which doesn't suffer from catastrophic b…
skirpichev May 29, 2021
b131e51
Merge branch 'main' into fix-44258
skirpichev May 30, 2021
db9652e
revert denom -> den
skirpichev May 30, 2021
6336aef
strip "_" from the decimal str, add few tests
skirpichev May 30, 2021
b11ef1e
drop redundant tests
skirpichev May 30, 2021
5f7e32a
Add versionchanged & whatsnew entry
skirpichev May 30, 2021
983b67d
Amend Fraction constructor docs
skirpichev May 30, 2021
076b396
Change .. versionchanged:...
skirpichev May 31, 2021
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
7 changes: 6 additions & 1 deletion Doc/library/fractions.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,8 @@ another rational number, or from a string.

where the optional ``sign`` may be either '+' or '-' and
``numerator`` and ``denominator`` (if present) are strings of
decimal digits. In addition, any string that represents a finite
decimal digits (underscores may be used to delimit digits as with
integral literals in code). In addition, any string that represents a finite
value and is accepted by the :class:`float` constructor is also
accepted by the :class:`Fraction` constructor. In either form the
input string may also have leading and/or trailing whitespace.
Expand Down Expand Up @@ -89,6 +90,10 @@ another rational number, or from a string.
and *denominator*. :func:`math.gcd` always return a :class:`int` type.
Previously, the GCD type depended on *numerator* and *denominator*.

.. versionchanged:: 3.11
Underscores are now permitted when creating a :class:`Fraction` instance
from a string, following :PEP:`515` rules.

.. attribute:: numerator

Numerator of the Fraction in lowest term.
Expand Down
5 changes: 5 additions & 0 deletions Doc/whatsnew/3.11.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,11 @@ New Modules
Improved Modules
================

fractions
---------

Support :PEP:`515`-style initialization of :class:`~fractions.Fraction` from
string. (Contributed by Sergey B Kirpichev in :issue:`44258`.)

Optimizations
=============
Expand Down
21 changes: 11 additions & 10 deletions Lib/fractions.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -21,17 +21,17 @@
_PyHASH_INF = sys.hash_info.inf

_RATIONAL_FORMAT = re.compile(r"""
\A\s* # optional whitespace at the start, then
(?P<sign>[-+]?) # an optional sign, then
(?=\d|\.\d) # lookahead for digit or .digit
(?P<num>\d*) # numerator (possibly empty)
(?: # followed by
(?:/(?P<denom>\d+))? # an optional denominator
| # or
(?:\.(?P<decimal>\d*))? # an optional fractional part
(?:E(?P<exp>[-+]?\d+))? # and optional exponent
\A\s* # optional whitespace at the start,
(?P<sign>[-+]?) # an optional sign, then
(?=\d|\.\d) # lookahead for digit or .digit
(?P<num>\d*|\d+(_\d+)*) # numerator (possibly empty)
(?: # followed by
(?:/(?P<denom>\d+(_\d+)*))? # an optional denominator
| # or
(?:\.(?P<decimal>d*|\d+(_\d+)*))? # an optional fractional part
(?:E(?P<exp>[-+]?\d+(_\d+)*))? # and optional exponent
)
\s*\Z # and optional whitespace to finish
\s*\Z # and optional whitespace to finish
""", re.VERBOSE | re.IGNORECASE)


Expand Down Expand Up @@ -122,6 +122,7 @@ def __new__(cls, numerator=0, denominator=None, *, _normalize=True):
denominator = 1
decimal = m.group('decimal')
if decimal:
decimal = decimal.replace('_', '')
scale = 10**len(decimal)
numerator = numerator * scale + int(decimal)
denominator *= scale
Expand Down
62 changes: 62 additions & 0 deletions Lib/test/test_fractions.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -173,6 +173,12 @@ def testFromString(self):
self.assertEqual((-12300, 1), _components(F("-1.23e4")))
self.assertEqual((0, 1), _components(F(" .0e+0\t")))
self.assertEqual((0, 1), _components(F("-0.000e0")))
self.assertEqual((123, 1), _components(F("1_2_3")))
self.assertEqual((41, 107), _components(F("1_2_3/3_2_1")))
self.assertEqual((6283, 2000), _components(F("3.14_15")))
self.assertEqual((6283, 2*10**13), _components(F("3.14_15e-1_0")))
self.assertEqual((101, 100), _components(F("1.01")))
self.assertEqual((101, 100), _components(F("1.0_1")))

self.assertRaisesMessage(
ZeroDivisionError, "Fraction(3, 0)",
Expand Down Expand Up @@ -210,6 +216,62 @@ def testFromString(self):
# Allow 3. and .3, but not .
ValueError, "Invalid literal for Fraction: '.'",
F, ".")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '_'",
F, "_")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '_1'",
F, "_1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1__2'",
F, "1__2")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '/_'",
F, "/_")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1_/'",
F, "1_/")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '_1/'",
F, "_1/")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1__2/'",
F, "1__2/")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/_'",
F, "1/_")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/_1'",
F, "1/_1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/1__2'",
F, "1/1__2")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1._111'",
F, "1._111")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1.1__1'",
F, "1.1__1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1.1e+_1'",
F, "1.1e+_1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1.1e+1__1'",
F, "1.1e+1__1")
# Test catastrophic backtracking.
val = "9"*50 + "_"
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '" + val + "'",
F, val)
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/" + val + "'",
F, "1/" + val)
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1." + val + "'",
F, "1." + val)
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1.1+e" + val + "'",
F, "1.1+e" + val)

def testImmutable(self):
r = F(7, 3)
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2021-05-28-09-43-33.bpo-44258.nh5F7R.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Support PEP 515 for Fraction's initialization from string.