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

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merged 11 commits into from
Jun 7, 2021
Merged

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

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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
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31 changes: 16 additions & 15 deletions Lib/fractions.py
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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<den>\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 @@ -115,15 +115,16 @@ def __new__(cls, numerator=0, denominator=None, *, _normalize=True):
raise ValueError('Invalid literal for Fraction: %r' %
numerator)
numerator = int(m.group('num') or '0')
denom = m.group('denom')
if denom:
denominator = int(denom)
denominator = m.group('den')
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I'd suggest reverting this set of changes; IIUC they're not needed for this PR, and I don't see any particular advantage to the rename. (In fact, I prefer the version where we don't have the same local name referring to both a string and an int.)

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@skirpichev skirpichev May 30, 2021 •
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I don't see any particular advantage to the rename.

Naming of patterns seems to be more consistent in this case: num/den vs num/denom.

But you are right, this is not related to the PR. I'll revert.

I prefer the version where we don't have the same local name referring to both a string and an int

I don't think there are. We have den/denom for strings and denominator - which is an integer.

This patch may be better:

diff --git a/Lib/fractions.py b/Lib/fractions.py
index 180cd94c28..1268b6bd27 100644
--- a/Lib/fractions.py
+++ b/Lib/fractions.py
@@ -26,7 +26,7 @@
     (?=\d|\.\d)                           # lookahead for digit or .digit
     (?P<num>\d*|\d+(_\d+)*)               # numerator (possibly empty)
     (?:                                   # followed by
-       (?:/(?P<denom>\d+(_\d+)*))?        # an optional denominator
+       (?:/(?P<den>\d+(_\d+)*))?          # an optional denominator
     |                                     # or
        (?:\.(?P<decimal>d*|\d+(_\d+)*))?  # an optional fractional part
        (?:E(?P<exp>[-+]?\d+(_\d+)*))?     # and optional exponent
@@ -115,9 +115,9 @@ def __new__(cls, numerator=0, denominator=None, *, _normalize=True):
                     raise ValueError('Invalid literal for Fraction: %r' %
                                      numerator)
                 numerator = int(m.group('num') or '0')
-                denom = m.group('denom')
-                if denom:
-                    denominator = int(denom)
+                den = m.group('den')
+                if den:
+                    denominator = int(den)
                 else:
                     denominator = 1
                     decimal = m.group('decimal')

if denominator:
denominator = int(denominator)
else:
denominator = 1
decimal = m.group('decimal')
if decimal:
scale = 10**len(decimal)
numerator = numerator * scale + int(decimal)
decimal = int(decimal)
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scale = 10**len(str(decimal))
numerator = numerator * scale + decimal
denominator *= scale
exp = m.group('exp')
if exp:
Expand Down
72 changes: 72 additions & 0 deletions Lib/test/test_fractions.py
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Expand Up @@ -173,6 +173,10 @@ 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.assertRaisesMessage(
ZeroDivisionError, "Fraction(3, 0)",
Expand Down Expand Up @@ -210,6 +214,74 @@ 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'",
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'",
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: '1.1_'",
F, "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_'",
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
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@@ -0,0 +1 @@
Support PEP 515 for Fraction's initialization from string.