diff --git a/Doc/library/fractions.rst b/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
   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 +90,10 @@ 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*.

   .. attribute:: numerator

      Numerator of the Fraction in lowest term.

@@ -86,6 +86,11 @@ New Modules
Improved Modules
================


Optimizations
=============

diff --git a/Lib/fractions.py b/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
    )
-    \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:
                        scale = 10**len(decimal)
                        numerator = numerator * scale + int(decimal)
                        denominator *= scale

diff --git a/Lib/test/test_fractions.py b/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.assertRaisesMessage(
            ZeroDivisionError, "Fraction(3, 0)",
@@ -210,6 +216,62 @@ def testFromString(self):
            # Allow 3. and .3, but not .
            ValueError, "Invalid literal for Fraction: '.'",
            F, ".")

    def testImmutable(self):
        r = F(7, 3)