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

Doc/library/fractions.rst

@@ -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.
@@ -89,6 +90,9 @@ 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
+ Supported :PEP:`515`-style initialization from string.
+
  .. attribute:: numerator
 
  Numerator of the Fraction in lowest term.

Doc/whatsnew/3.11.rst

@@ -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
 =============

Lib/fractions.py

@@ -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)
 
 
@@ -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

Lib/test/test_fractions.py

@@ -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)",
@@ -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)

Misc/NEWS.d/next/Library/2021-05-28-09-43-33.bpo-44258.nh5F7R.rst

@@ -0,0 +1 @@
+Support PEP 515 for Fraction's initialization from string.