diff --git a/CHANGES.rst b/CHANGES.rst
index 71f7b98..c36d861 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,6 +1,12 @@
 ChangeLog
 =========
 
+1.14 (2022-01-11)
+-----------------
+
+* Implement ``__format__`` for ``Fraction``, following
+  https://github.com/python/cpython/pull/100161
+
 1.13 (2022-01-11)
 -----------------
 
diff --git a/src/quicktions.pyx b/src/quicktions.pyx
index 5a4915b..2fdc6ff 100644
--- a/src/quicktions.pyx
+++ b/src/quicktions.pyx
@@ -38,13 +38,14 @@ cdef extern from *:
     cdef long long PY_LLONG_MIN, PY_LLONG_MAX
     cdef long long MAX_SMALL_NUMBER "(PY_LLONG_MAX / 100)"
 
-cdef object Rational, Integral, Real, Complex, Decimal, math, operator, sys
+cdef object Rational, Integral, Real, Complex, Decimal, math, operator, re, sys
 cdef object PY_MAX_LONG_LONG = PY_LLONG_MAX
 
 from numbers import Rational, Integral, Real, Complex
 from decimal import Decimal
 import math
 import operator
+import re
 import sys
 
 cdef bint _decimal_supports_integer_ratio = hasattr(Decimal, "as_integer_ratio")  # Py3.6+
@@ -237,6 +238,99 @@ except AttributeError:  # pre Py3.2
     _PyHASH_INF = hash(float('+inf'))
 
 
+# Helpers for formatting
+
+cdef _round_to_exponent(n, d, exponent, bint no_neg_zero=False):
+    """Round a rational number to the nearest multiple of a given power of 10.
+
+    Rounds the rational number n/d to the nearest integer multiple of
+    10**exponent, rounding to the nearest even integer multiple in the case of
+    a tie. Returns a pair (sign: bool, significand: int) representing the
+    rounded value (-1)**sign * significand * 10**exponent.
+
+    If no_neg_zero is true, then the returned sign will always be False when
+    the significand is zero. Otherwise, the sign reflects the sign of the
+    input.
+
+    d must be positive, but n and d need not be relatively prime.
+    """
+    if exponent >= 0:
+        d *= 10**exponent
+    else:
+        n *= 10**-exponent
+
+    # The divmod quotient is correct for round-ties-towards-positive-infinity;
+    # In the case of a tie, we zero out the least significant bit of q.
+    q, r = divmod(n + (d >> 1), d)
+    if r == 0 and d & 1 == 0:
+        q &= -2
+
+    cdef bint sign = q < 0 if no_neg_zero else n < 0
+    return sign, abs(q)
+
+
+cdef _round_to_figures(n, d, Py_ssize_t figures):
+    """Round a rational number to a given number of significant figures.
+
+    Rounds the rational number n/d to the given number of significant figures
+    using the round-ties-to-even rule, and returns a triple
+    (sign: bool, significand: int, exponent: int) representing the rounded
+    value (-1)**sign * significand * 10**exponent.
+
+    In the special case where n = 0, returns a significand of zero and
+    an exponent of 1 - figures, for compatibility with formatting.
+    Otherwise, the returned significand satisfies
+    10**(figures - 1) <= significand < 10**figures.
+
+    d must be positive, but n and d need not be relatively prime.
+    figures must be positive.
+    """
+    # Special case for n == 0.
+    if n == 0:
+        return False, 0, 1 - figures
+
+    cdef bint sign
+
+    # Find integer m satisfying 10**(m - 1) <= abs(n)/d <= 10**m. (If abs(n)/d
+    # is a power of 10, either of the two possible values for m is fine.)
+    str_n, str_d = str(abs(n)), str(d)
+    cdef Py_ssize_t m = len(str_n) - len(str_d) + (str_d <= str_n)
+
+    # Round to a multiple of 10**(m - figures). The significand we get
+    # satisfies 10**(figures - 1) <= significand <= 10**figures.
+    exponent = m - figures
+    sign, significand = _round_to_exponent(n, d, exponent)
+
+    # Adjust in the case where significand == 10**figures, to ensure that
+    # 10**(figures - 1) <= significand < 10**figures.
+    if len(str(significand)) == figures + 1:
+        significand //= 10
+        exponent += 1
+
+    return sign, significand, exponent
+
+
+# Pattern for matching float-style format specifications;
+# supports 'e', 'E', 'f', 'F', 'g', 'G' and '%' presentation types.
+cdef object _FLOAT_FORMAT_SPECIFICATION_MATCHER = re.compile(r"""
+    (?:
+        (?P<fill>.)?
+        (?P<align>[<>=^])
+    )?
+    (?P<sign>[-+ ]?)
+    (?P<no_neg_zero>z)?
+    (?P<alt>\#)?
+    # A '0' that's *not* followed by another digit is parsed as a minimum width
+    # rather than a zeropad flag.
+    (?P<zeropad>0(?=[0-9]))?
+    (?P<minimumwidth>0|[1-9][0-9]*)?
+    (?P<thousands_sep>[,_])?
+    (?:\.(?P<precision>0|[1-9][0-9]*))?
+    (?P<presentation_type>[eEfFgG%])
+    $
+""", re.DOTALL | re.VERBOSE).match
+
+
 cdef class Fraction:
     """A Rational number.
 
@@ -495,9 +589,132 @@ cdef class Fraction:
         """str(self)"""
         if self._denominator == 1:
             return str(self._numerator)
+        elif PY_MAJOR_VERSION > 2:
+            return f'{self._numerator}/{self._denominator}'
         else:
             return '%s/%s' % (self._numerator, self._denominator)
 
+    def __format__(self, format_spec, /):
+        """Format this fraction according to the given format specification."""
+
+        # Backwards compatibility with existing formatting.
+        if not format_spec:
+            return str(self)
+
+        # Validate and parse the format specifier.
+        match = _FLOAT_FORMAT_SPECIFICATION_MATCHER(format_spec)
+        if match is None:
+            raise ValueError(
+                f"Invalid format specifier {format_spec!r} "
+                f"for object of type {type(self).__name__!r}"
+            )
+        match = match.groupdict()  # Py2
+        if match["align"] is not None and match["zeropad"] is not None:
+            # Avoid the temptation to guess.
+            raise ValueError(
+                f"Invalid format specifier {format_spec!r} "
+                f"for object of type {type(self).__name__!r}; "
+                "can't use explicit alignment when zero-padding"
+            )
+        fill = match["fill"] or " "
+        align = match["align"] or ">"
+        pos_sign = "" if match["sign"] == "-" else match["sign"]
+        cdef bint no_neg_zero = match["no_neg_zero"]
+        cdef bint alternate_form = match["alt"]
+        cdef bint zeropad = match["zeropad"]
+        cdef Py_ssize_t minimumwidth = int(match["minimumwidth"] or "0")
+        thousands_sep = match["thousands_sep"]
+        cdef Py_ssize_t precision = int(match["precision"] or "6")
+        cdef Py_UCS4 presentation_type = ord(match["presentation_type"])
+        cdef bint trim_zeros = presentation_type in u"gG" and not alternate_form
+        cdef bint trim_point = not alternate_form
+        exponent_indicator = "E" if presentation_type in u"EFG" else "e"
+
+        cdef bint negative, scientific
+        cdef Py_ssize_t exponent, figures
+
+        # Round to get the digits we need, figure out where to place the point,
+        # and decide whether to use scientific notation. 'point_pos' is the
+        # relative to the _end_ of the digit string: that is, it's the number
+        # of digits that should follow the point.
+        if presentation_type in u"fF%":
+            exponent = -precision
+            if presentation_type == u"%":
+                exponent -= 2
+            negative, significand = _round_to_exponent(
+                self._numerator, self._denominator, exponent, no_neg_zero)
+            scientific = False
+            point_pos = precision
+        else:  # presentation_type in "eEgG"
+            figures = (
+                max(precision, 1)
+                if presentation_type in u"gG"
+                else precision + 1
+            )
+            negative, significand, exponent = _round_to_figures(
+                self._numerator, self._denominator, figures)
+            scientific = (
+                presentation_type in u"eE"
+                or exponent > 0
+                or exponent + figures <= -4
+            )
+            point_pos = figures - 1 if scientific else -exponent
+
+        # Get the suffix - the part following the digits, if any.
+        if presentation_type == u"%":
+            suffix = "%"
+        elif scientific:
+            #suffix = f"{exponent_indicator}{exponent + point_pos:+03d}"
+            suffix = "%s%+03d" % (exponent_indicator, exponent + point_pos)
+        else:
+            suffix = ""
+
+        # String of output digits, padded sufficiently with zeros on the left
+        # so that we'll have at least one digit before the decimal point.
+        digits = f"{significand:0{point_pos + 1}d}"
+
+        # Before padding, the output has the form f"{sign}{leading}{trailing}",
+        # where `leading` includes thousands separators if necessary and
+        # `trailing` includes the decimal separator where appropriate.
+        sign = "-" if negative else pos_sign
+        leading = digits[: len(digits) - point_pos]
+        frac_part = digits[len(digits) - point_pos :]
+        if trim_zeros:
+            frac_part = frac_part.rstrip("0")
+        separator = "" if trim_point and not frac_part else "."
+        trailing = separator + frac_part + suffix
+
+        # Do zero padding if required.
+        if zeropad:
+            min_leading = minimumwidth - len(sign) - len(trailing)
+            # When adding thousands separators, they'll be added to the
+            # zero-padded portion too, so we need to compensate.
+            leading = leading.zfill(
+                3 * min_leading // 4 + 1 if thousands_sep else min_leading
+            )
+
+        # Insert thousands separators if required.
+        if thousands_sep:
+            first_pos = 1 + (len(leading) - 1) % 3
+            leading = leading[:first_pos] + "".join([
+                thousands_sep + leading[pos : pos + 3]
+                for pos in range(first_pos, len(leading), 3)
+            ])
+
+        # We now have a sign and a body. Pad with fill character if necessary
+        # and return.
+        body = leading + trailing
+        padding = fill * (minimumwidth - len(sign) - len(body))
+        if align == ">":
+            return padding + sign + body
+        elif align == "<":
+            return sign + body + padding
+        elif align == "^":
+            half = len(padding) // 2
+            return padding[:half] + sign + body + padding[half:]
+        else:  # align == "="
+            return sign + padding + body
+
     def __add__(a, b):
         """a + b"""
         return forward(a, b, _add, _math_op_add)
@@ -1211,7 +1428,9 @@ cdef enum ParserState:
 
 cdef _raise_invalid_input(s):
     s = repr(s)
-    if s[0] == 'b':
+    if s[:2] in ('b"', "b'"):
+        s = s[1:]
+    elif PY_MAJOR_VERSION ==2 and s[:2] in ('u"', "u'"):
         s = s[1:]
     raise ValueError(f'Invalid literal for Fraction: {s}') from None
 
diff --git a/src/test_fractions.py b/src/test_fractions.py
index e3071bc..e640193 100644
--- a/src/test_fractions.py
+++ b/src/test_fractions.py
@@ -8,8 +8,9 @@
 
 """Tests for Lib/fractions.py, slightly adapted for quicktions."""
 
-from __future__ import division
+from __future__ import division, unicode_literals
 
+import contextlib
 from decimal import Decimal
 try:
     from test.support import requires_IEEE_754
@@ -193,6 +194,15 @@ def assertRaisesMessage(self, exc_type, message,
         else:
             self.fail("%s not raised" % exc_type.__name__)
 
+    try:
+        unittest.TestCase.subTest
+    except AttributeError:
+        @contextlib.contextmanager
+        def subTest(self, **kw):
+            yield
+
+    ##########
+
     def testInit(self):
         self.assertEqual((0, 1), _components(F()))
         self.assertEqual((7, 1), _components(F(7)))
@@ -982,6 +992,382 @@ def denominator(self):
         self.assertEqual(type(f.numerator), myint)
         self.assertEqual(type(f.denominator), myint)
 
+    def test_format_no_presentation_type(self):
+        # Triples (fraction, specification, expected_result)
+        testcases = [
+            (F(1, 3), '', '1/3'),
+            (F(-1, 3), '', '-1/3'),
+            (F(3), '', '3'),
+            (F(-3), '', '-3'),
+        ]
+        for fraction, spec, expected in testcases:
+            with self.subTest(fraction=fraction, spec=spec):
+                self.assertEqual(format(fraction, spec), expected)
+
+    def test_format_e_presentation_type(self):
+        # Triples (fraction, specification, expected_result)
+        testcases = [
+            (F(2, 3), '.6e', '6.666667e-01'),
+            (F(3, 2), '.6e', '1.500000e+00'),
+            (F(2, 13), '.6e', '1.538462e-01'),
+            (F(2, 23), '.6e', '8.695652e-02'),
+            (F(2, 33), '.6e', '6.060606e-02'),
+            (F(13, 2), '.6e', '6.500000e+00'),
+            (F(20, 2), '.6e', '1.000000e+01'),
+            (F(23, 2), '.6e', '1.150000e+01'),
+            (F(33, 2), '.6e', '1.650000e+01'),
+            (F(2, 3), '.6e', '6.666667e-01'),
+            (F(3, 2), '.6e', '1.500000e+00'),
+            # Zero
+            (F(0), '.3e', '0.000e+00'),
+            # Powers of 10, to exercise the log10 boundary logic
+            (F(1, 1000), '.3e', '1.000e-03'),
+            (F(1, 100), '.3e', '1.000e-02'),
+            (F(1, 10), '.3e', '1.000e-01'),
+            (F(1, 1), '.3e', '1.000e+00'),
+            (F(10), '.3e', '1.000e+01'),
+            (F(100), '.3e', '1.000e+02'),
+            (F(1000), '.3e', '1.000e+03'),
+            # Boundary where we round up to the next power of 10
+            (F('99.999994999999'), '.6e', '9.999999e+01'),
+            (F('99.999995'), '.6e', '1.000000e+02'),
+            (F('99.999995000001'), '.6e', '1.000000e+02'),
+            # Negatives
+            (F(-2, 3), '.6e', '-6.666667e-01'),
+            (F(-3, 2), '.6e', '-1.500000e+00'),
+            (F(-100), '.6e', '-1.000000e+02'),
+            # Large and small
+            (F('1e1000'), '.3e', '1.000e+1000'),
+            (F('1e-1000'), '.3e', '1.000e-1000'),
+            # Using 'E' instead of 'e' should give us a capital 'E'
+            (F(2, 3), '.6E', '6.666667E-01'),
+            # Tiny precision
+            (F(2, 3), '.1e', '6.7e-01'),
+            (F('0.995'), '.0e', '1e+00'),
+            # Default precision is 6
+            (F(22, 7), 'e', '3.142857e+00'),
+            # Alternate form forces a decimal point
+            (F('0.995'), '#.0e', '1.e+00'),
+            # Check that padding takes the exponent into account.
+            (F(22, 7), '11.6e', '3.142857e+00'),
+            (F(22, 7), '12.6e', '3.142857e+00'),
+            (F(22, 7), '13.6e', ' 3.142857e+00'),
+            # Thousands separators
+            (F('1234567.123456'), ',.5e', '1.23457e+06'),
+            (F('123.123456'), '012_.2e', '0_001.23e+02'),
+            # z flag is legal, but never makes a difference to the output
+            (F(-1, 7**100), 'z.6e', '-3.091690e-85'),
+        ]
+        for fraction, spec, expected in testcases:
+            with self.subTest(fraction=fraction, spec=spec):
+                self.assertEqual(format(fraction, spec), expected)
+
+    def test_format_f_presentation_type(self):
+        # Triples (fraction, specification, expected_result)
+        testcases = [
+            # Simple .f formatting
+            (F(0, 1), '.2f', '0.00'),
+            (F(1, 3), '.2f', '0.33'),
+            (F(2, 3), '.2f', '0.67'),
+            (F(4, 3), '.2f', '1.33'),
+            (F(1, 8), '.2f', '0.12'),
+            (F(3, 8), '.2f', '0.38'),
+            (F(1, 13), '.2f', '0.08'),
+            (F(1, 199), '.2f', '0.01'),
+            (F(1, 200), '.2f', '0.00'),
+            (F(22, 7), '.5f', '3.14286'),
+            (F('399024789'), '.2f', '399024789.00'),
+            # Large precision (more than float can provide)
+            (F(104348, 33215), '.50f',
+             '3.14159265392142104470871594159265392142104470871594'),
+            # Precision defaults to 6 if not given
+            (F(22, 7), 'f', '3.142857'),
+            (F(0), 'f', '0.000000'),
+            (F(-22, 7), 'f', '-3.142857'),
+            # Round-ties-to-even checks
+            (F('1.225'), '.2f', '1.22'),
+            (F('1.2250000001'), '.2f', '1.23'),
+            (F('1.2349999999'), '.2f', '1.23'),
+            (F('1.235'), '.2f', '1.24'),
+            (F('1.245'), '.2f', '1.24'),
+            (F('1.2450000001'), '.2f', '1.25'),
+            (F('1.2549999999'), '.2f', '1.25'),
+            (F('1.255'), '.2f', '1.26'),
+            (F('-1.225'), '.2f', '-1.22'),
+            (F('-1.2250000001'), '.2f', '-1.23'),
+            (F('-1.2349999999'), '.2f', '-1.23'),
+            (F('-1.235'), '.2f', '-1.24'),
+            (F('-1.245'), '.2f', '-1.24'),
+            (F('-1.2450000001'), '.2f', '-1.25'),
+            (F('-1.2549999999'), '.2f', '-1.25'),
+            (F('-1.255'), '.2f', '-1.26'),
+            # Negatives and sign handling
+            (F(2, 3), '.2f', '0.67'),
+            (F(2, 3), '-.2f', '0.67'),
+            (F(2, 3), '+.2f', '+0.67'),
+            (F(2, 3), ' .2f', ' 0.67'),
+            (F(-2, 3), '.2f', '-0.67'),
+            (F(-2, 3), '-.2f', '-0.67'),
+            (F(-2, 3), '+.2f', '-0.67'),
+            (F(-2, 3), ' .2f', '-0.67'),
+            # Formatting to zero places
+            (F(1, 2), '.0f', '0'),
+            (F(-1, 2), '.0f', '-0'),
+            (F(22, 7), '.0f', '3'),
+            (F(-22, 7), '.0f', '-3'),
+            # Formatting to zero places, alternate form
+            (F(1, 2), '#.0f', '0.'),
+            (F(-1, 2), '#.0f', '-0.'),
+            (F(22, 7), '#.0f', '3.'),
+            (F(-22, 7), '#.0f', '-3.'),
+            # z flag for suppressing negative zeros
+            (F('-0.001'), 'z.2f', '0.00'),
+            (F('-0.001'), '-z.2f', '0.00'),
+            (F('-0.001'), '+z.2f', '+0.00'),
+            (F('-0.001'), ' z.2f', ' 0.00'),
+            (F('0.001'), 'z.2f', '0.00'),
+            (F('0.001'), '-z.2f', '0.00'),
+            (F('0.001'), '+z.2f', '+0.00'),
+            (F('0.001'), ' z.2f', ' 0.00'),
+            # Specifying a minimum width
+            (F(2, 3), '6.2f', '  0.67'),
+            (F(12345), '6.2f', '12345.00'),
+            (F(12345), '12f', '12345.000000'),
+            # Fill and alignment
+            (F(2, 3), '>6.2f', '  0.67'),
+            (F(2, 3), '<6.2f', '0.67  '),
+            (F(2, 3), '^3.2f', '0.67'),
+            (F(2, 3), '^4.2f', '0.67'),
+            (F(2, 3), '^5.2f', '0.67 '),
+            (F(2, 3), '^6.2f', ' 0.67 '),
+            (F(2, 3), '^7.2f', ' 0.67  '),
+            (F(2, 3), '^8.2f', '  0.67  '),
+            # '=' alignment
+            (F(-2, 3), '=+8.2f', '-   0.67'),
+            (F(2, 3), '=+8.2f', '+   0.67'),
+            # Fill character
+            (F(-2, 3), 'X>3.2f', '-0.67'),
+            (F(-2, 3), 'X>7.2f', 'XX-0.67'),
+            (F(-2, 3), 'X<7.2f', '-0.67XX'),
+            (F(-2, 3), 'X^7.2f', 'X-0.67X'),
+            (F(-2, 3), 'X=7.2f', '-XX0.67'),
+            (F(-2, 3), ' >7.2f', '  -0.67'),
+            # Corner cases: weird fill characters
+            (F(-2, 3), '\x00>7.2f', '\x00\x00-0.67'),
+            (F(-2, 3), '\n>7.2f', '\n\n-0.67'),
+            (F(-2, 3), '\t>7.2f', '\t\t-0.67'),
+            (F(-2, 3), '>>7.2f', '>>-0.67'),
+            (F(-2, 3), '<>7.2f', '<<-0.67'),
+            (F(-2, 3), '→>7.2f', '→→-0.67'),
+            # Zero-padding
+            (F(-2, 3), '07.2f', '-000.67'),
+            (F(-2, 3), '-07.2f', '-000.67'),
+            (F(2, 3), '+07.2f', '+000.67'),
+            (F(2, 3), ' 07.2f', ' 000.67'),
+            # An isolated zero is a minimum width, not a zero-pad flag.
+            # So unlike zero-padding, it's legal in combination with alignment.
+            (F(2, 3), '0.2f', '0.67'),
+            (F(2, 3), '>0.2f', '0.67'),
+            (F(2, 3), '<0.2f', '0.67'),
+            (F(2, 3), '^0.2f', '0.67'),
+            (F(2, 3), '=0.2f', '0.67'),
+            # Corner case: zero-padding _and_ a zero minimum width.
+            (F(2, 3), '00.2f', '0.67'),
+            # Thousands separator (only affects portion before the point)
+            (F(2, 3), ',.2f', '0.67'),
+            (F(2, 3), ',.7f', '0.6666667'),
+            (F('123456.789'), ',.2f', '123,456.79'),
+            (F('1234567'), ',.2f', '1,234,567.00'),
+            (F('12345678'), ',.2f', '12,345,678.00'),
+            (F('12345678'), ',f', '12,345,678.000000'),
+            # Underscore as thousands separator
+            (F(2, 3), '_.2f', '0.67'),
+            (F(2, 3), '_.7f', '0.6666667'),
+            (F('123456.789'), '_.2f', '123_456.79'),
+            (F('1234567'), '_.2f', '1_234_567.00'),
+            (F('12345678'), '_.2f', '12_345_678.00'),
+            # Thousands and zero-padding
+            (F('1234.5678'), '07,.2f', '1,234.57'),
+            (F('1234.5678'), '08,.2f', '1,234.57'),
+            (F('1234.5678'), '09,.2f', '01,234.57'),
+            (F('1234.5678'), '010,.2f', '001,234.57'),
+            (F('1234.5678'), '011,.2f', '0,001,234.57'),
+            (F('1234.5678'), '012,.2f', '0,001,234.57'),
+            (F('1234.5678'), '013,.2f', '00,001,234.57'),
+            (F('1234.5678'), '014,.2f', '000,001,234.57'),
+            (F('1234.5678'), '015,.2f', '0,000,001,234.57'),
+            (F('1234.5678'), '016,.2f', '0,000,001,234.57'),
+            (F('-1234.5678'), '07,.2f', '-1,234.57'),
+            (F('-1234.5678'), '08,.2f', '-1,234.57'),
+            (F('-1234.5678'), '09,.2f', '-1,234.57'),
+            (F('-1234.5678'), '010,.2f', '-01,234.57'),
+            (F('-1234.5678'), '011,.2f', '-001,234.57'),
+            (F('-1234.5678'), '012,.2f', '-0,001,234.57'),
+            (F('-1234.5678'), '013,.2f', '-0,001,234.57'),
+            (F('-1234.5678'), '014,.2f', '-00,001,234.57'),
+            (F('-1234.5678'), '015,.2f', '-000,001,234.57'),
+            (F('-1234.5678'), '016,.2f', '-0,000,001,234.57'),
+            # Corner case: no decimal point
+            (F('-1234.5678'), '06,.0f', '-1,235'),
+            (F('-1234.5678'), '07,.0f', '-01,235'),
+            (F('-1234.5678'), '08,.0f', '-001,235'),
+            (F('-1234.5678'), '09,.0f', '-0,001,235'),
+            # Corner-case - zero-padding specified through fill and align
+            # instead of the zero-pad character - in this case, treat '0' as a
+            # regular fill character and don't attempt to insert commas into
+            # the filled portion. This differs from the int and float
+            # behaviour.
+            (F('1234.5678'), '0=12,.2f', '00001,234.57'),
+            # Corner case where it's not clear whether the '0' indicates zero
+            # padding or gives the minimum width, but there's still an obvious
+            # answer to give. We want this to work in case the minimum width
+            # is being inserted programmatically: spec = f'{width}.2f'.
+            (F('12.34'), '0.2f', '12.34'),
+            (F('12.34'), 'X>0.2f', '12.34'),
+            # 'F' should work identically to 'f'
+            (F(22, 7), '.5F', '3.14286'),
+            # %-specifier
+            (F(22, 7), '.2%', '314.29%'),
+            (F(1, 7), '.2%', '14.29%'),
+            (F(1, 70), '.2%', '1.43%'),
+            (F(1, 700), '.2%', '0.14%'),
+            (F(1, 7000), '.2%', '0.01%'),
+            (F(1, 70000), '.2%', '0.00%'),
+            (F(1, 7), '.0%', '14%'),
+            (F(1, 7), '#.0%', '14.%'),
+            (F(100, 7), ',.2%', '1,428.57%'),
+            (F(22, 7), '7.2%', '314.29%'),
+            (F(22, 7), '8.2%', ' 314.29%'),
+            (F(22, 7), '08.2%', '0314.29%'),
+            # Test cases from #67790 and discuss.python.org Ideas thread.
+            (F(1, 3), '.2f', '0.33'),
+            (F(1, 8), '.2f', '0.12'),
+            (F(3, 8), '.2f', '0.38'),
+            (F(2545, 1000), '.2f', '2.54'),
+            (F(2549, 1000), '.2f', '2.55'),
+            (F(2635, 1000), '.2f', '2.64'),
+            (F(1, 100), '.1f', '0.0'),
+            (F(49, 1000), '.1f', '0.0'),
+            (F(51, 1000), '.1f', '0.1'),
+            (F(149, 1000), '.1f', '0.1'),
+            (F(151, 1000), '.1f', '0.2'),
+        ]
+        for fraction, spec, expected in testcases:
+            with self.subTest(fraction=fraction, spec=spec):
+                self.assertEqual(format(fraction, spec), expected)
+
+    def test_format_g_presentation_type(self):
+        # Triples (fraction, specification, expected_result)
+        testcases = [
+            (F('0.000012345678'), '.6g', '1.23457e-05'),
+            (F('0.00012345678'), '.6g', '0.000123457'),
+            (F('0.0012345678'), '.6g', '0.00123457'),
+            (F('0.012345678'), '.6g', '0.0123457'),
+            (F('0.12345678'), '.6g', '0.123457'),
+            (F('1.2345678'), '.6g', '1.23457'),
+            (F('12.345678'), '.6g', '12.3457'),
+            (F('123.45678'), '.6g', '123.457'),
+            (F('1234.5678'), '.6g', '1234.57'),
+            (F('12345.678'), '.6g', '12345.7'),
+            (F('123456.78'), '.6g', '123457'),
+            (F('1234567.8'), '.6g', '1.23457e+06'),
+            # Rounding up cases
+            (F('9.99999e+2'), '.4g', '1000'),
+            (F('9.99999e-8'), '.4g', '1e-07'),
+            (F('9.99999e+8'), '.4g', '1e+09'),
+            # Check round-ties-to-even behaviour
+            (F('-0.115'), '.2g', '-0.12'),
+            (F('-0.125'), '.2g', '-0.12'),
+            (F('-0.135'), '.2g', '-0.14'),
+            (F('-0.145'), '.2g', '-0.14'),
+            (F('0.115'), '.2g', '0.12'),
+            (F('0.125'), '.2g', '0.12'),
+            (F('0.135'), '.2g', '0.14'),
+            (F('0.145'), '.2g', '0.14'),
+            # Trailing zeros and decimal point suppressed by default ...
+            (F(0), '.6g', '0'),
+            (F('123.400'), '.6g', '123.4'),
+            (F('123.000'), '.6g', '123'),
+            (F('120.000'), '.6g', '120'),
+            (F('12000000'), '.6g', '1.2e+07'),
+            # ... but not when alternate form is in effect
+            (F(0), '#.6g', '0.00000'),
+            (F('123.400'), '#.6g', '123.400'),
+            (F('123.000'), '#.6g', '123.000'),
+            (F('120.000'), '#.6g', '120.000'),
+            (F('12000000'), '#.6g', '1.20000e+07'),
+            # 'G' format (uses 'E' instead of 'e' for the exponent indicator)
+            (F('123.45678'), '.6G', '123.457'),
+            (F('1234567.8'), '.6G', '1.23457E+06'),
+            # Default precision is 6 significant figures
+            (F('3.1415926535'), 'g', '3.14159'),
+            # Precision 0 is treated the same as precision 1.
+            (F('0.000031415'), '.0g', '3e-05'),
+            (F('0.00031415'), '.0g', '0.0003'),
+            (F('0.31415'), '.0g', '0.3'),
+            (F('3.1415'), '.0g', '3'),
+            (F('3.1415'), '#.0g', '3.'),
+            (F('31.415'), '.0g', '3e+01'),
+            (F('31.415'), '#.0g', '3.e+01'),
+            (F('0.000031415'), '.1g', '3e-05'),
+            (F('0.00031415'), '.1g', '0.0003'),
+            (F('0.31415'), '.1g', '0.3'),
+            (F('3.1415'), '.1g', '3'),
+            (F('3.1415'), '#.1g', '3.'),
+            (F('31.415'), '.1g', '3e+01'),
+            # Thousands separator
+            (F(2**64), '_.25g', '18_446_744_073_709_551_616'),
+            # As with 'e' format, z flag is legal, but has no effect
+            (F(-1, 7**100), 'zg', '-3.09169e-85'),
+        ]
+        for fraction, spec, expected in testcases:
+            with self.subTest(fraction=fraction, spec=spec):
+                self.assertEqual(format(fraction, spec), expected)
+
+    def test_invalid_formats(self):
+        fraction = F(2, 3)
+        with self.assertRaises(TypeError):
+            format(fraction, None)
+
+        invalid_specs = [
+            'Q6f',  # regression test
+            # illegal to use fill or alignment when zero padding
+            'X>010f',
+            'X<010f',
+            'X^010f',
+            'X=010f',
+            '0>010f',
+            '0<010f',
+            '0^010f',
+            '0=010f',
+            '>010f',
+            '<010f',
+            '^010f',
+            '=010e',
+            '=010f',
+            '=010g',
+            '=010%',
+            '>00.2f',
+            '>00f',
+            # Too many zeros - minimum width should not have leading zeros
+            '006f',
+            # Leading zeros in precision
+            '.010f',
+            '.02f',
+            '.000f',
+            # Missing precision
+            '.e',
+            '.f',
+            '.g',
+            '.%',
+            # Z instead of z for negative zero suppression
+            'Z.2f'
+        ]
+        for spec in invalid_specs:
+            with self.subTest(spec=spec):
+                with self.assertRaises(ValueError):
+                    format(fraction, spec)
+
 
 class QuicktionsTest(unittest.TestCase):
     _pi = (