from collections import abc
from itertools import combinations
import array
import gc
import math
import operator
import unittest
import struct
import sys
import warnings
import weakref

from test import support
from test.support import import_helper
from test.support.script_helper import assert_python_ok
from test.support.testcase import ComplexesAreIdenticalMixin

ISBIGENDIAN = sys.byteorder == "big"

integer_codes = 'b', 'B', 'h', 'H', 'i', 'I', 'l', 'L', 'q', 'Q', 'n', 'N'
byteorders = '', '@', '=', '<', '>', '!'

INF = float('inf')
NAN = float('nan')

def iter_integer_formats(byteorders=byteorders):
    for code in integer_codes:
        for byteorder in byteorders:
            if (byteorder not in ('', '@') and code in ('n', 'N')):
                continue
            yield code, byteorder

def string_reverse(s):
    return s[::-1]

def bigendian_to_native(value):
    if ISBIGENDIAN:
        return value
    else:
        return string_reverse(value)

class StructTest(ComplexesAreIdenticalMixin, unittest.TestCase):
    def test_isbigendian(self):
        self.assertEqual((struct.pack('=i', 1)[0] == 0), ISBIGENDIAN)

    def test_consistence(self):
        self.assertRaises(struct.error, struct.calcsize, 'Z')

        sz = struct.calcsize('i')
        self.assertEqual(sz * 3, struct.calcsize('iii'))

        fmt = 'cbxxxxxxhhhhiillffd?'
        fmt3 = '3c3b18x12h6i6l6f3d3?'
        sz = struct.calcsize(fmt)
        sz3 = struct.calcsize(fmt3)
        self.assertEqual(sz * 3, sz3)

        self.assertRaises(struct.error, struct.pack, 'iii', 3)
        self.assertRaises(struct.error, struct.pack, 'i', 3, 3, 3)
        self.assertRaises((TypeError, struct.error), struct.pack, 'i', 'foo')
        self.assertRaises((TypeError, struct.error), struct.pack, 'P', 'foo')
        self.assertRaises(struct.error, struct.unpack, 'd', b'flap')
        s = struct.pack('ii', 1, 2)
        self.assertRaises(struct.error, struct.unpack, 'iii', s)
        self.assertRaises(struct.error, struct.unpack, 'i', s)

    def test_transitiveness(self):
        c = b'a'
        b = 1
        h = 255
        i = 65535
        l = 65536
        f = 3.1415
        d = 3.1415
        t = True

        for prefix in ('', '@', '<', '>', '=', '!'):
            for format in ('xcbhilfd?', 'xcBHILfd?'):
                format = prefix + format
                s = struct.pack(format, c, b, h, i, l, f, d, t)
                cp, bp, hp, ip, lp, fp, dp, tp = struct.unpack(format, s)
                self.assertEqual(cp, c)
                self.assertEqual(bp, b)
                self.assertEqual(hp, h)
                self.assertEqual(ip, i)
                self.assertEqual(lp, l)
                self.assertEqual(int(100 * fp), int(100 * f))
                self.assertEqual(int(100 * dp), int(100 * d))
                self.assertEqual(tp, t)

    def test_new_features(self):
        # Test some of the new features in detail
        # (format, argument, big-endian result, little-endian result, asymmetric)
        tests = [
            ('c', b'a', b'a', b'a', 0),
            ('xc', b'a', b'\0a', b'\0a', 0),
            ('cx', b'a', b'a\0', b'a\0', 0),
            ('s', b'a', b'a', b'a', 0),
            ('0s', b'helloworld', b'', b'', 1),
            ('1s', b'helloworld', b'h', b'h', 1),
            ('9s', b'helloworld', b'helloworl', b'helloworl', 1),
            ('10s', b'helloworld', b'helloworld', b'helloworld', 0),
            ('11s', b'helloworld', b'helloworld\0', b'helloworld\0', 1),
            ('20s', b'helloworld', b'helloworld'+10*b'\0', b'helloworld'+10*b'\0', 1),
            ('0p', b'helloworld', b'', b'', 1),
            ('1p', b'helloworld', b'\x00', b'\x00', 1),
            ('2p', b'helloworld', b'\x01h', b'\x01h', 1),
            ('10p', b'helloworld', b'\x09helloworl', b'\x09helloworl', 1),
            ('11p', b'helloworld', b'\x0Ahelloworld', b'\x0Ahelloworld', 0),
            ('12p', b'helloworld', b'\x0Ahelloworld\0', b'\x0Ahelloworld\0', 1),
            ('20p', b'helloworld', b'\x0Ahelloworld'+9*b'\0', b'\x0Ahelloworld'+9*b'\0', 1),
            ('b', 7, b'\7', b'\7', 0),
            ('b', -7, b'\371', b'\371', 0),
            ('B', 7, b'\7', b'\7', 0),
            ('B', 249, b'\371', b'\371', 0),
            ('h', 700, b'\002\274', b'\274\002', 0),
            ('h', -700, b'\375D', b'D\375', 0),
            ('H', 700, b'\002\274', b'\274\002', 0),
            ('H', 0x10000-700, b'\375D', b'D\375', 0),
            ('i', 70000000, b'\004,\035\200', b'\200\035,\004', 0),
            ('i', -70000000, b'\373\323\342\200', b'\200\342\323\373', 0),
            ('I', 70000000, b'\004,\035\200', b'\200\035,\004', 0),
            ('I', 0x100000000-70000000, b'\373\323\342\200', b'\200\342\323\373', 0),
            ('l', 70000000, b'\004,\035\200', b'\200\035,\004', 0),
            ('l', -70000000, b'\373\323\342\200', b'\200\342\323\373', 0),
            ('L', 70000000, b'\004,\035\200', b'\200\035,\004', 0),
            ('L', 0x100000000-70000000, b'\373\323\342\200', b'\200\342\323\373', 0),
            ('f', 2.0, b'@\000\000\000', b'\000\000\000@', 0),
            ('d', 2.0, b'@\000\000\000\000\000\000\000',
                       b'\000\000\000\000\000\000\000@', 0),
            ('f', -2.0, b'\300\000\000\000', b'\000\000\000\300', 0),
            ('d', -2.0, b'\300\000\000\000\000\000\000\000',
                        b'\000\000\000\000\000\000\000\300', 0),
            ('?', 0, b'\0', b'\0', 0),
            ('?', 3, b'\1', b'\1', 1),
            ('?', True, b'\1', b'\1', 0),
            ('?', [], b'\0', b'\0', 1),
            ('?', (1,), b'\1', b'\1', 1),
        ]

        for fmt, arg, big, lil, asy in tests:
            for (xfmt, exp) in [('>'+fmt, big), ('!'+fmt, big), ('<'+fmt, lil),
                                ('='+fmt, ISBIGENDIAN and big or lil)]:
                res = struct.pack(xfmt, arg)
                self.assertEqual(res, exp)
                self.assertEqual(struct.calcsize(xfmt), len(res))
                rev = struct.unpack(xfmt, res)[0]
                if rev != arg:
                    self.assertTrue(asy)

    def test_calcsize(self):
        expected_size = {
            'b': 1, 'B': 1,
            'h': 2, 'H': 2,
            'i': 4, 'I': 4,
            'l': 4, 'L': 4,
            'q': 8, 'Q': 8,
            }

        # standard integer sizes
        for code, byteorder in iter_integer_formats(('=', '<', '>', '!')):
            format = byteorder+code
            size = struct.calcsize(format)
            self.assertEqual(size, expected_size[code])

        # native integer sizes
        native_pairs = 'bB', 'hH', 'iI', 'lL', 'nN', 'qQ'
        for format_pair in native_pairs:
            for byteorder in '', '@':
                signed_size = struct.calcsize(byteorder + format_pair[0])
                unsigned_size = struct.calcsize(byteorder + format_pair[1])
                self.assertEqual(signed_size, unsigned_size)

        # bounds for native integer sizes
        self.assertEqual(struct.calcsize('b'), 1)
        self.assertLessEqual(2, struct.calcsize('h'))
        self.assertLessEqual(4, struct.calcsize('l'))
        self.assertLessEqual(struct.calcsize('h'), struct.calcsize('i'))
        self.assertLessEqual(struct.calcsize('i'), struct.calcsize('l'))
        self.assertLessEqual(8, struct.calcsize('q'))
        self.assertLessEqual(struct.calcsize('l'), struct.calcsize('q'))
        self.assertGreaterEqual(struct.calcsize('n'), struct.calcsize('i'))
        self.assertGreaterEqual(struct.calcsize('n'), struct.calcsize('P'))

    def test_cache_bytes_vs_str_bb(self):
        # Mixing str and bytes formats must not raise BytesWarning under -bb.
        code = (
            'import struct\n'
            'struct.calcsize(b"!d"); struct.calcsize("!d")\n'
            'struct.calcsize(">d"); struct.calcsize(b">d")\n'
            'struct.Struct(b"i"); struct.Struct("i")\n'
        )
        assert_python_ok('-bb', '-c', code)

    def test_integers(self):
        # Integer tests (bBhHiIlLqQnN).
        import binascii

        class IntTester(unittest.TestCase):
            def __init__(self, format):
                super(IntTester, self).__init__(methodName='test_one')
                self.format = format
                self.code = format[-1]
                self.byteorder = format[:-1]
                if not self.byteorder in byteorders:
                    raise ValueError("unrecognized packing byteorder: %s" %
                                     self.byteorder)
                self.bytesize = struct.calcsize(format)
                self.bitsize = self.bytesize * 8
                if self.code in tuple('bhilqn'):
                    self.signed = True
                    self.min_value = -(2**(self.bitsize-1))
                    self.max_value = 2**(self.bitsize-1) - 1
                elif self.code in tuple('BHILQN'):
                    self.signed = False
                    self.min_value = 0
                    self.max_value = 2**self.bitsize - 1
                else:
                    raise ValueError("unrecognized format code: %s" %
                                     self.code)

            def test_one(self, x, pack=struct.pack,
                                  unpack=struct.unpack,
                                  unhexlify=binascii.unhexlify):

                format = self.format
                if self.min_value <= x <= self.max_value:
                    expected = x
                    if self.signed and x < 0:
                        expected += 1 << self.bitsize
                    self.assertGreaterEqual(expected, 0)
                    expected = '%x' % expected
                    if len(expected) & 1:
                        expected = "0" + expected
                    expected = expected.encode('ascii')
                    expected = unhexlify(expected)
                    expected = (b"\x00" * (self.bytesize - len(expected)) +
                                expected)
                    if (self.byteorder == '<' or
                        self.byteorder in ('', '@', '=') and not ISBIGENDIAN):
                        expected = string_reverse(expected)
                    self.assertEqual(len(expected), self.bytesize)

                    # Pack work?
                    got = pack(format, x)
                    self.assertEqual(got, expected)

                    # Unpack work?
                    retrieved = unpack(format, got)[0]
                    self.assertEqual(x, retrieved)

                    # Adding any byte should cause a "too big" error.
                    self.assertRaises((struct.error, TypeError), unpack, format,
                                                                 b'\x01' + got)
                else:
                    # x is out of range -- verify pack realizes that.
                    self.assertRaises((OverflowError, ValueError, struct.error),
                                      pack, format, x)

            def run(self):
                from random import randrange

                # Create all interesting powers of 2.
                values = []
                for exp in range(self.bitsize + 3):
                    values.append(1 << exp)

                # Add some random values.
                for i in range(self.bitsize):
                    val = 0
                    for j in range(self.bytesize):
                        val = (val << 8) | randrange(256)
                    values.append(val)

                # Values absorbed from other tests
                values.extend([300, 700000, sys.maxsize*4])

                # Try all those, and their negations, and +-1 from
                # them.  Note that this tests all power-of-2
                # boundaries in range, and a few out of range, plus
                # +-(2**n +- 1).
                for base in values:
                    for val in -base, base:
                        for incr in -1, 0, 1:
                            x = val + incr
                            self.test_one(x)

                # Some error cases.
                class NotAnInt:
                    def __int__(self):
                        return 42

                # Objects with an '__index__' method should be allowed
                # to pack as integers.  That is assuming the implemented
                # '__index__' method returns an 'int'.
                class Indexable(object):
                    def __init__(self, value):
                        self._value = value

                    def __index__(self):
                        return self._value

                # If the '__index__' method raises a type error, then
                # '__int__' should be used with a deprecation warning.
                class BadIndex(object):
                    def __index__(self):
                        raise TypeError

                    def __int__(self):
                        return 42

                self.assertRaises((TypeError, struct.error),
                                  struct.pack, self.format,
                                  "a string")
                self.assertRaises((TypeError, struct.error),
                                  struct.pack, self.format,
                                  randrange)
                self.assertRaises((TypeError, struct.error),
                                  struct.pack, self.format,
                                  3+42j)
                self.assertRaises((TypeError, struct.error),
                                  struct.pack, self.format,
                                  NotAnInt())
                self.assertRaises((TypeError, struct.error),
                                  struct.pack, self.format,
                                  BadIndex())

                # Check for legitimate values from '__index__'.
                for obj in (Indexable(0), Indexable(10), Indexable(17),
                            Indexable(42), Indexable(100), Indexable(127)):
                    try:
                        struct.pack(format, obj)
                    except:
                        self.fail("integer code pack failed on object "
                                  "with '__index__' method")

                # Check for bogus values from '__index__'.
                for obj in (Indexable(b'a'), Indexable('b'), Indexable(None),
                            Indexable({'a': 1}), Indexable([1, 2, 3])):
                    self.assertRaises((TypeError, struct.error),
                                      struct.pack, self.format,
                                      obj)

        for code, byteorder in iter_integer_formats():
            format = byteorder+code
            t = IntTester(format)
            t.run()

    def test_nN_code(self):
        # n and N don't exist in standard sizes
        def assertStructError(func, *args, **kwargs):
            with self.assertRaises(struct.error) as cm:
                func(*args, **kwargs)
            self.assertIn("bad char in struct format", str(cm.exception))
        for code in 'nN':
            for byteorder in ('=', '<', '>', '!'):
                format = byteorder+code
                assertStructError(struct.calcsize, format)
                assertStructError(struct.pack, format, 0)
                assertStructError(struct.unpack, format, b"")

    def test_p_code(self):
        # Test p ("Pascal string") code.
        for code, input, expected, expectedback in [
                ('0p', b'abc', b'',                b''),
                ('p',  b'abc', b'\x00',            b''),
                ('1p', b'abc', b'\x00',            b''),
                ('2p', b'abc', b'\x01a',           b'a'),
                ('3p', b'abc', b'\x02ab',          b'ab'),
                ('4p', b'abc', b'\x03abc',         b'abc'),
                ('5p', b'abc', b'\x03abc\x00',     b'abc'),
                ('6p', b'abc', b'\x03abc\x00\x00', b'abc'),
                ('1000p', b'x'*1000, b'\xff' + b'x'*999, b'x'*255)]:
            got = struct.pack(code, input)
            self.assertEqual(got, expected)
            (got,) = struct.unpack(code, got)
            self.assertEqual(got, expectedback)

    def test_705836(self):
        # SF bug 705836.  "<f" and ">f" had a severe rounding bug, where a carry
        # from the low-order discarded bits could propagate into the exponent
        # field, causing the result to be wrong by a factor of 2.
        for base in range(1, 33):
            # smaller <- largest representable float less than base.
            delta = 0.5
            while base - delta / 2.0 != base:
                delta /= 2.0
            smaller = base - delta
            # Packing this rounds away a solid string of trailing 1 bits.
            packed = struct.pack("<f", smaller)
            unpacked = struct.unpack("<f", packed)[0]
            # This failed at base = 2, 4, and 32, with unpacked = 1, 2, and
            # 16, respectively.
            self.assertEqual(base, unpacked)
            bigpacked = struct.pack(">f", smaller)
            self.assertEqual(bigpacked, string_reverse(packed))
            unpacked = struct.unpack(">f", bigpacked)[0]
            self.assertEqual(base, unpacked)

        # Largest finite IEEE single.
        big = (1 << 24) - 1
        big = math.ldexp(big, 127 - 23)
        packed = struct.pack(">f", big)
        unpacked = struct.unpack(">f", packed)[0]
        self.assertEqual(big, unpacked)

        # The same, but tack on a 1 bit so it rounds up to infinity.
        big = (1 << 25) - 1
        big = math.ldexp(big, 127 - 24)
        self.assertRaises(OverflowError, struct.pack, ">f", big)
        self.assertRaises(OverflowError, struct.pack, "<f", big)
        # same for native format, see gh-145633
        self.assertRaises(OverflowError, struct.pack, "f", big)

        # And for half-floats
        big = (1 << 11) - 1
        big = math.ldexp(big, 15 - 10)
        packed = struct.pack(">e", big)
        unpacked = struct.unpack(">e", packed)[0]
        self.assertEqual(big, unpacked)
        big = (1 << 12) - 1
        big = math.ldexp(big, 15 - 11)
        self.assertRaises(OverflowError, struct.pack, ">e", big)
        self.assertRaises(OverflowError, struct.pack, "<e", big)
        self.assertRaises(OverflowError, struct.pack, "e", big)

    def test_1530559(self):
        for code, byteorder in iter_integer_formats():
            format = byteorder + code
            self.assertRaises(struct.error, struct.pack, format, 1.0)
            self.assertRaises(struct.error, struct.pack, format, 1.5)
        self.assertRaises(struct.error, struct.pack, 'P', 1.0)
        self.assertRaises(struct.error, struct.pack, 'P', 1.5)

    def test_unpack_from(self):
        test_string = b'abcd01234'
        fmt = '4s'
        s = struct.Struct(fmt)
        for cls in (bytes, bytearray):
            data = cls(test_string)
            self.assertEqual(s.unpack_from(data), (b'abcd',))
            self.assertEqual(s.unpack_from(data, 2), (b'cd01',))
            self.assertEqual(s.unpack_from(data, 4), (b'0123',))
            for i in range(6):
                self.assertEqual(s.unpack_from(data, i), (data[i:i+4],))
            for i in range(6, len(test_string) + 1):
                self.assertRaises(struct.error, s.unpack_from, data, i)
        for cls in (bytes, bytearray):
            data = cls(test_string)
            self.assertEqual(struct.unpack_from(fmt, data), (b'abcd',))
            self.assertEqual(struct.unpack_from(fmt, data, 2), (b'cd01',))
            self.assertEqual(struct.unpack_from(fmt, data, 4), (b'0123',))
            for i in range(6):
                self.assertEqual(struct.unpack_from(fmt, data, i), (data[i:i+4],))
            for i in range(6, len(test_string) + 1):
                self.assertRaises(struct.error, struct.unpack_from, fmt, data, i)

        # keyword arguments
        self.assertEqual(s.unpack_from(buffer=test_string, offset=2),
                         (b'cd01',))

    def _test_pack_into(self, pack_into):
        test_string = b'Reykjavik rocks, eow!'
        writable_buf = memoryview(array.array('b', b' '*100))

        # Test without offset
        pack_into(writable_buf, 0, test_string)
        from_buf = writable_buf.tobytes()[:len(test_string)]
        self.assertEqual(from_buf, test_string)

        # Test with offset.
        pack_into(writable_buf, 10, test_string)
        from_buf = writable_buf.tobytes()[:len(test_string)+10]
        self.assertEqual(from_buf, test_string[:10] + test_string)

        # Test with negative offset.
        pack_into(writable_buf, -30, test_string)
        from_buf = writable_buf.tobytes()[-30:-30+len(test_string)]
        self.assertEqual(from_buf, test_string)

        # Go beyond boundaries.
        small_buf = array.array('b', b' '*10)
        with self.assertRaises((ValueError, struct.error)):
            pack_into(small_buf, 0, test_string)
        with self.assertRaises((ValueError, struct.error)):
            pack_into(writable_buf, 90, test_string)
        with self.assertRaises((ValueError, struct.error)):
            pack_into(writable_buf, -10, test_string)
        with self.assertRaises((ValueError, struct.error)):
            pack_into(writable_buf, 150, test_string)
        with self.assertRaises((ValueError, struct.error)):
            pack_into(writable_buf, -150, test_string)

        # Test invalid buffer.
        self.assertRaises(TypeError, pack_into, b' '*100, 0, test_string)
        self.assertRaises(TypeError, pack_into, ' '*100, 0, test_string)
        self.assertRaises(TypeError, pack_into, [0]*100, 0, test_string)
        self.assertRaises(TypeError, pack_into, None, 0, test_string)
        self.assertRaises(TypeError, pack_into, writable_buf[::2], 0, test_string)
        self.assertRaises(TypeError, pack_into, writable_buf[::-1], 0, test_string)

        # Test bogus offset (issue bpo-3694)
        with self.assertRaises(TypeError):
            pack_into(writable_buf, None, test_string)
        with self.assertRaises(TypeError):
            pack_into(writable_buf, 0.0, test_string)
        with self.assertRaises(OverflowError):
            pack_into(writable_buf, 2**1000, test_string)
        with self.assertRaises(OverflowError):
            pack_into(writable_buf, -2**1000, test_string)

    def test_pack_into(self):
        s = struct.Struct('21s')
        self._test_pack_into(s.pack_into)

    def test_pack_into_fn(self):
        pack_into = lambda *args: struct.pack_into('21s', *args)
        self._test_pack_into(pack_into)

    def test_unpack_with_buffer(self):
        # SF bug 1563759: struct.unpack doesn't support buffer protocol objects
        data1 = array.array('B', b'\x12\x34\x56\x78')
        data2 = memoryview(b'\x12\x34\x56\x78') # XXX b'......XXXX......', 6, 4
        for data in [data1, data2]:
            value, = struct.unpack('>I', data)
            self.assertEqual(value, 0x12345678)

    def test_bool(self):
        class ExplodingBool(object):
            def __bool__(self):
                raise OSError
        for prefix in tuple("<>!=")+('',):
            false = (), [], [], '', 0
            true = [1], 'test', 5, -1, 0xffffffff+1, 0xffffffff/2

            falseFormat = prefix + '?' * len(false)
            packedFalse = struct.pack(falseFormat, *false)
            unpackedFalse = struct.unpack(falseFormat, packedFalse)

            trueFormat = prefix + '?' * len(true)
            packedTrue = struct.pack(trueFormat, *true)
            unpackedTrue = struct.unpack(trueFormat, packedTrue)

            self.assertEqual(len(true), len(unpackedTrue))
            self.assertEqual(len(false), len(unpackedFalse))

            for t in unpackedFalse:
                self.assertFalse(t)
            for t in unpackedTrue:
                self.assertTrue(t)

            packed = struct.pack(prefix+'?', 1)

            self.assertEqual(len(packed), struct.calcsize(prefix+'?'))

            if len(packed) != 1:
                self.assertFalse(prefix, msg='encoded bool is not one byte: %r'
                                             %packed)

            try:
                struct.pack(prefix + '?', ExplodingBool())
            except OSError:
                pass
            else:
                self.fail("Expected OSError: struct.pack(%r, "
                          "ExplodingBool())" % (prefix + '?'))

        for c in [b'\x01', b'\x7f', b'\xff', b'\x0f', b'\xf0']:
            self.assertTrue(struct.unpack('>?', c)[0])
            self.assertTrue(struct.unpack('<?', c)[0])
            self.assertTrue(struct.unpack('=?', c)[0])
            self.assertTrue(struct.unpack('@?', c)[0])

    def test_count_overflow(self):
        hugecount = '{}b'.format(sys.maxsize+1)
        self.assertRaises(struct.error, struct.calcsize, hugecount)

        hugecount2 = '{}b{}H'.format(sys.maxsize//2, sys.maxsize//2)
        self.assertRaises(struct.error, struct.calcsize, hugecount2)

        hugecount3 = '{}i{}q'.format(sys.maxsize // 4, sys.maxsize // 8)
        self.assertRaises(struct.error, struct.calcsize, hugecount3)

        hugecount4 = '{}?s'.format(sys.maxsize)
        self.assertRaises(struct.error, struct.calcsize, hugecount4)

        hugecount5 = '{}?p'.format(sys.maxsize)
        self.assertRaises(struct.error, struct.calcsize, hugecount5)

    def test_trailing_counter(self):
        store = array.array('b', b' '*100)

        # format lists containing only count spec should result in an error
        self.assertRaises(struct.error, struct.pack, '12345')
        self.assertRaises(struct.error, struct.unpack, '12345', b'')
        self.assertRaises(struct.error, struct.pack_into, '12345', store, 0)
        self.assertRaises(struct.error, struct.unpack_from, '12345', store, 0)

        # Format lists with trailing count spec should result in an error
        self.assertRaises(struct.error, struct.pack, 'c12345', 'x')
        self.assertRaises(struct.error, struct.unpack, 'c12345', b'x')
        self.assertRaises(struct.error, struct.pack_into, 'c12345', store, 0,
                           'x')
        self.assertRaises(struct.error, struct.unpack_from, 'c12345', store,
                           0)

        # Mixed format tests
        self.assertRaises(struct.error, struct.pack, '14s42', 'spam and eggs')
        self.assertRaises(struct.error, struct.unpack, '14s42',
                          b'spam and eggs')
        self.assertRaises(struct.error, struct.pack_into, '14s42', store, 0,
                          'spam and eggs')
        self.assertRaises(struct.error, struct.unpack_from, '14s42', store, 0)

    def test_Struct_reinitialization(self):
        # Issue 9422: there was a memory leak when reinitializing a
        # Struct instance.  This test can be used to detect the leak
        # when running with regrtest -L.
        s = struct.Struct('>h')
        msg = 'Re-initialization .* will not work'
        with self.assertWarnsRegex(FutureWarning, msg):
            s.__init__('>hh')
        self.assertEqual(s.format, '>hh')
        packed = b'\x00\x01\x00\x02'
        self.assertEqual(s.pack(1, 2), packed)
        self.assertEqual(s.unpack(packed), (1, 2))

        s.__init__('>hh')  # same format
        self.assertEqual(s.format, '>hh')
        self.assertEqual(s.pack(1, 2), packed)
        self.assertEqual(s.unpack(packed), (1, 2))

        with self.assertWarnsRegex(FutureWarning, msg):
            with self.assertRaises(ValueError):
                s.__init__('\udc00')
        self.assertEqual(s.format, '>hh')
        self.assertEqual(s.pack(1, 2), packed)
        self.assertEqual(s.unpack(packed), (1, 2))

        with self.assertWarnsRegex(FutureWarning, msg):
            with self.assertRaises(struct.error):
                s.__init__('$')
        self.assertEqual(s.format, '>hh')
        self.assertEqual(s.pack(1, 2), packed)
        self.assertEqual(s.unpack(packed), (1, 2))

    def check_sizeof(self, format_str, number_of_codes):
        # The size of 'PyStructObject'
        totalsize = support.calcobjsize('2n3P?0P')
        # The size taken up by the 'formatcode' dynamic array
        totalsize += struct.calcsize('P3n0P') * (number_of_codes + 1)
        support.check_sizeof(self, struct.Struct(format_str), totalsize)

    @support.cpython_only
    def test__sizeof__(self):
        for code in integer_codes:
            self.check_sizeof(code, 1)
        self.check_sizeof('BHILfdspP', 9)
        self.check_sizeof('B' * 1234, 1234)
        self.check_sizeof('fd', 2)
        self.check_sizeof('xxxxxxxxxxxxxx', 0)
        self.check_sizeof('100H', 1)
        self.check_sizeof('187s', 1)
        self.check_sizeof('20p', 1)
        self.check_sizeof('0s', 1)
        self.check_sizeof('0p', 1)
        self.check_sizeof('0c', 0)

    def test_boundary_error_message(self):
        regex1 = (
            r'pack_into requires a buffer of at least 6 '
            r'bytes for packing 1 bytes at offset 5 '
            r'\(actual buffer size is 1\)'
        )
        with self.assertRaisesRegex(struct.error, regex1):
            struct.pack_into('b', bytearray(1), 5, 1)

        regex2 = (
            r'unpack_from requires a buffer of at least 6 '
            r'bytes for unpacking 1 bytes at offset 5 '
            r'\(actual buffer size is 1\)'
        )
        with self.assertRaisesRegex(struct.error, regex2):
            struct.unpack_from('b', bytearray(1), 5)

    def test_boundary_error_message_with_negative_offset(self):
        byte_list = bytearray(10)
        with self.assertRaisesRegex(
                struct.error,
                r'no space to pack 4 bytes at offset -2'):
            struct.pack_into('<I', byte_list, -2, 123)

        with self.assertRaisesRegex(
                struct.error,
                'offset -11 out of range for 10-byte buffer'):
            struct.pack_into('<B', byte_list, -11, 123)

        with self.assertRaisesRegex(
                struct.error,
                r'not enough data to unpack 4 bytes at offset -2'):
            struct.unpack_from('<I', byte_list, -2)

        with self.assertRaisesRegex(
                struct.error,
                "offset -11 out of range for 10-byte buffer"):
            struct.unpack_from('<B', byte_list, -11)

    def test_boundary_error_message_with_large_offset(self):
        # Test overflows cause by large offset and value size (issue 30245)
        regex1 = (
            r'pack_into requires a buffer of at least ' + str(sys.maxsize + 4) +
            r' bytes for packing 4 bytes at offset ' + str(sys.maxsize) +
            r' \(actual buffer size is 10\)'
        )
        with self.assertRaisesRegex(struct.error, regex1):
            struct.pack_into('<I', bytearray(10), sys.maxsize, 1)

        regex2 = (
            r'unpack_from requires a buffer of at least ' + str(sys.maxsize + 4) +
            r' bytes for unpacking 4 bytes at offset ' + str(sys.maxsize) +
            r' \(actual buffer size is 10\)'
        )
        with self.assertRaisesRegex(struct.error, regex2):
            struct.unpack_from('<I', bytearray(10), sys.maxsize)

    def test_issue29802(self):
        # When the second argument of struct.unpack() was of wrong type
        # the Struct object was decrefed twice and the reference to
        # deallocated object was left in a cache.
        with self.assertRaises(TypeError):
            struct.unpack('b', 0)
        # Shouldn't crash.
        self.assertEqual(struct.unpack('b', b'a'), (b'a'[0],))

    def test_format_attr(self):
        s = struct.Struct('=i2H')
        self.assertEqual(s.format, '=i2H')

        # use a bytes string
        s2 = struct.Struct(s.format.encode())
        self.assertEqual(s2.format, s.format)

    def test_struct_cleans_up_at_runtime_shutdown(self):
        code = """if 1:
            import struct

            class C:
                def __init__(self):
                    self.pack = struct.pack
                def __del__(self):
                    self.pack('I', -42)

            struct.x = C()
            """
        rc, stdout, stderr = assert_python_ok("-c", code)
        self.assertEqual(rc, 0)
        self.assertEqual(stdout.rstrip(), b"")
        self.assertIn(b"Exception ignored while calling deallocator", stderr)
        self.assertIn(b"C.__del__", stderr)

    def test__struct_reference_cycle_cleaned_up(self):
        # Regression test for python/cpython#94207.

        # When we create a new struct module, trigger use of its cache,
        # and then delete it ...
        _struct_module = import_helper.import_fresh_module("_struct")
        module_ref = weakref.ref(_struct_module)
        _struct_module.calcsize("b")
        del _struct_module

        # Then the module should have been garbage collected.
        gc.collect()
        self.assertIsNone(
            module_ref(), "_struct module was not garbage collected")

    @support.cpython_only
    def test__struct_types_immutable(self):
        # See https://github.com/python/cpython/issues/94254

        Struct = struct.Struct
        unpack_iterator = type(struct.iter_unpack("b", b'x'))
        for cls in (Struct, unpack_iterator):
            with self.subTest(cls=cls):
                with self.assertRaises(TypeError):
                    cls.x = 1


    def test_issue35714(self):
        # Embedded null characters should not be allowed in format strings.
        for s in '\0', '2\0i', b'\0':
            with self.assertRaisesRegex(struct.error,
                                        'embedded null character'):
                struct.calcsize(s)

    @support.cpython_only
    def test_issue98248(self):
        def test_error_msg(prefix, int_type, is_unsigned):
            fmt_str = prefix + int_type
            size = struct.calcsize(fmt_str)
            if is_unsigned:
                max_ = 2 ** (size * 8) - 1
                min_ = 0
            else:
                max_ = 2 ** (size * 8 - 1) - 1
                min_ = -2 ** (size * 8 - 1)
            error_msg = f"'{int_type}' format requires {min_} <= number <= {max_}"
            for number in [int(-1e50), min_ - 1, max_ + 1, int(1e50)]:
                with self.subTest(format_str=fmt_str, number=number):
                    with self.assertRaisesRegex(struct.error, error_msg):
                        struct.pack(fmt_str, number)
            error_msg = "required argument is not an integer"
            not_number = ""
            with self.subTest(format_str=fmt_str, number=not_number):
                with self.assertRaisesRegex(struct.error, error_msg):
                    struct.pack(fmt_str, not_number)

        for prefix in '@=<>':
            for int_type in 'BHILQ':
                test_error_msg(prefix, int_type, True)
            for int_type in 'bhilq':
                test_error_msg(prefix, int_type, False)

        int_type = 'N'
        test_error_msg('@', int_type, True)

        int_type = 'n'
        test_error_msg('@', int_type, False)

    @support.cpython_only
    def test_issue98248_error_propagation(self):
        class Div0:
            def __index__(self):
                1 / 0

        def test_error_propagation(fmt_str):
            with self.subTest(format_str=fmt_str, exception="ZeroDivisionError"):
                with self.assertRaises(ZeroDivisionError):
                    struct.pack(fmt_str, Div0())

        for prefix in '@=<>':
            for int_type in 'BHILQbhilq':
                test_error_propagation(prefix + int_type)

        test_error_propagation('N')
        test_error_propagation('n')

    def test_custom_struct_init(self):
        # Regression test for https://github.com/python/cpython/issues/112358
        class MyStruct(struct.Struct):
            def __init__(self, *args, **kwargs):
                super().__init__('>h')

        my_struct = MyStruct('>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        my_struct = MyStruct(format='>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')

        warnmsg = r"Different format arguments for __new__\(\) and __init__\(\) methods of Struct"
        with self.assertWarnsRegex(FutureWarning, warnmsg):
            my_struct = MyStruct('<h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(FutureWarning, warnmsg):
            my_struct = MyStruct(format='<h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')

        warnmsg = r"Struct\(\) missing required argument 'format' \(pos 1\)"
        with self.assertWarnsRegex(DeprecationWarning, warnmsg):
            my_struct = MyStruct()
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg):
            my_struct = MyStruct(arg='>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')

        warnmsg = r"Struct\(\) takes at most 1 argument \(2 given\)"
        with self.assertWarnsRegex(DeprecationWarning, warnmsg):
            my_struct = MyStruct('>h', 42)
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg):
            my_struct = MyStruct('>h', arg=42)
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg):
            my_struct = MyStruct('>h', format=42)
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg):
            my_struct = MyStruct(format='>h', arg=42)
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')

        warnmsg = r"Invalid 'format' argument for Struct\.__new__\(\): "
        with self.assertWarnsRegex(DeprecationWarning, warnmsg + '.*must be'):
            my_struct = MyStruct(42)
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg + '.*must be'):
            my_struct = MyStruct(format=42)
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg + 'bad char'):
            my_struct = MyStruct('$')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg + 'bad char'):
            my_struct = MyStruct(format='$')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg + "non-ASCII"):
            my_struct = MyStruct('\udc00')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertWarnsRegex(DeprecationWarning, warnmsg + "non-ASCII"):
            my_struct = MyStruct(format='\udc00')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')

    def test_custom_struct_new(self):
        # New way, no warnings:
        class MyStruct(struct.Struct):
            def __new__(cls, *args, **kwargs):
                return super().__new__(cls, '>h')

        for format in '>h', '<h', 42, '$', '\u20ac', '\udc00', b'\xa4':
            with self.subTest(format=format):
                my_struct = MyStruct(format)
                self.assertEqual(my_struct.format, '>h')
                self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        my_struct = MyStruct(format='<h')
        self.assertEqual(my_struct.format, '>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        my_struct = MyStruct()
        self.assertEqual(my_struct.format, '>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        my_struct = MyStruct('<h', 42)
        self.assertEqual(my_struct.format, '>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')

    def test_custom_struct_new_and_init(self):
        # New way, no warnings:
        class MyStruct(struct.Struct):
            def __new__(cls, newargs, initargs):
                return super().__new__(cls, *newargs)
            def __init__(self, newargs, initargs):
                if initargs is not None:
                    super().__init__(*initargs)

        my_struct = MyStruct(('>h',), ('>h',))
        self.assertEqual(my_struct.format, '>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertRaises(TypeError):
            MyStruct((), ())
        with self.assertRaises(TypeError):
            MyStruct(('>h',), ())
        with self.assertRaises(TypeError):
            MyStruct((), ('>h',))
        with self.assertRaises(TypeError):
            MyStruct((42,), ('>h',))
        with self.assertWarns(FutureWarning):
            with self.assertRaises(TypeError):
                MyStruct(('>h',), (42,))
        with self.assertRaises(struct.error):
            MyStruct(('$',), ('>h',))
        with self.assertWarns(FutureWarning):
            with self.assertRaises(struct.error):
                MyStruct(('>h',), ('$',))
        with self.assertRaises(ValueError):
            MyStruct(('\udc00',), ('>h',))
        with self.assertRaises(ValueError):
            MyStruct((b'\xa4',), ('>h',))
        with self.assertWarns(FutureWarning):
            with self.assertRaises(ValueError):
                MyStruct(('>h',), ('\udc00',))
        with self.assertWarns(FutureWarning):
            with self.assertRaises(ValueError):
                MyStruct(('>h',), (b'\xa4',))
        with self.assertWarns(FutureWarning):
            my_struct = MyStruct(('>h',), ('<h',))
        self.assertEqual(my_struct.format, '<h')
        self.assertEqual(my_struct.pack(12345), b'\x39\x30')

    def test_no_custom_struct_new_or_init(self):
        class MyStruct(struct.Struct):
            pass

        my_struct = MyStruct('>h')
        self.assertEqual(my_struct.format, '>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        my_struct = MyStruct(format='>h')
        self.assertEqual(my_struct.format, '>h')
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
        with self.assertRaises(TypeError):
            MyStruct()
        with self.assertRaises(TypeError):
            MyStruct(42)
        with self.assertRaises(struct.error):
            MyStruct('$')
        with self.assertRaises(ValueError):
            MyStruct('\udc00')
        with self.assertRaises(ValueError):
            MyStruct(b'\xa4')
        with self.assertRaises(TypeError):
            MyStruct('>h', 42)
        with self.assertRaises(TypeError):
            MyStruct('>h', arg=42)
        with self.assertRaises(TypeError):
            MyStruct(arg=42)
        with self.assertRaises(TypeError):
            MyStruct('>h', format='>h')

    def test_repr(self):
        s = struct.Struct('=i2H')
        self.assertEqual(repr(s), f'Struct({s.format!r})')

    def test_c_complex_round_trip(self):
        values = [complex(*_) for _ in combinations([1, -1, 0.0, -0.0, 2,
                                                     -3, INF, -INF, NAN], 2)]
        for z in values:
            for f in ['Zf', 'Zd', '>Zf', '>Zd', '<Zf', '<Zd']:
                with self.subTest(z=z, format=f):
                    round_trip = struct.unpack(f, struct.pack(f, z))[0]
                    self.assertComplexesAreIdentical(z, round_trip)
        z = 1+1j
        for fmt in ['F', 'D', '>F', '>D', '<F', '<D']:
            with self.subTest(format=fmt):
                with warnings.catch_warnings():
                    warnings.simplefilter("error", DeprecationWarning)
                    self.assertRaises(DeprecationWarning, struct.pack, fmt, z)
                with warnings.catch_warnings():
                    with self.assertWarns(DeprecationWarning):
                        b = struct.pack(fmt, z)

                with warnings.catch_warnings():
                    warnings.simplefilter("error", DeprecationWarning)
                    self.assertRaises(DeprecationWarning, struct.unpack, fmt, b)
                with self.assertWarns(DeprecationWarning):
                    round_trip = struct.unpack(fmt, b)[0]
                self.assertComplexesAreIdentical(z, round_trip)

    @unittest.skipIf(
        support.is_android or support.is_apple_mobile,
        "Subinterpreters are not supported on Android and iOS"
    )
    def test_endian_table_init_subinterpreters(self):
        # Verify that the _struct extension module can be initialized
        # concurrently in subinterpreters (gh-140260).
        try:
            from concurrent.futures import InterpreterPoolExecutor
        except ImportError:
            raise unittest.SkipTest("InterpreterPoolExecutor not available")

        code = "import struct"
        with InterpreterPoolExecutor(max_workers=5) as executor:
            results = executor.map(exec, [code] * 5)
            self.assertListEqual(list(results), [None] * 5)

    def test_operations_on_half_initialized_Struct(self):
        S = struct.Struct.__new__(struct.Struct)

        spam = array.array('b', b' ')
        self.assertRaises(RuntimeError, S.iter_unpack, spam)
        self.assertRaises(RuntimeError, S.pack, 1)
        self.assertRaises(RuntimeError, S.pack_into, spam, 1)
        self.assertRaises(RuntimeError, S.unpack, spam)
        self.assertRaises(RuntimeError, S.unpack_from, spam)
        self.assertRaises(AttributeError, getattr, S, 'format')
        self.assertRaises(RuntimeError, S.__sizeof__)
        self.assertRaises(RuntimeError, repr, S)
        self.assertEqual(S.size, -1)

    def test_float_round_trip(self):
        for format in (
            "f", "<f", ">f",
            "d", "<d", ">d",
            "e", "<e", ">e",
        ):
            with self.subTest(format=format):
                f = struct.unpack(format, struct.pack(format, 1.5))[0]
                self.assertEqual(f, 1.5)
                f = struct.unpack(format, struct.pack(format, NAN))[0]
                self.assertTrue(math.isnan(f), f)
                f = struct.unpack(format, struct.pack(format, INF))[0]
                self.assertTrue(math.isinf(f), f)
                self.assertEqual(math.copysign(1.0, f), 1.0)
                f = struct.unpack(format, struct.pack(format, -INF))[0]
                self.assertTrue(math.isinf(f), f)
                self.assertEqual(math.copysign(1.0, f), -1.0)


class UnpackIteratorTest(unittest.TestCase):
    """
    Tests for iterative unpacking (struct.Struct.iter_unpack).
    """

    def test_construct(self):
        def _check_iterator(it):
            self.assertIsInstance(it, abc.Iterator)
            self.assertIsInstance(it, abc.Iterable)
        s = struct.Struct('>ibcp')
        it = s.iter_unpack(b"")
        _check_iterator(it)
        it = s.iter_unpack(b"1234567")
        _check_iterator(it)
        # Wrong bytes length
        with self.assertRaises(struct.error):
            s.iter_unpack(b"123456")
        with self.assertRaises(struct.error):
            s.iter_unpack(b"12345678")
        # Zero-length struct
        s = struct.Struct('>')
        with self.assertRaises(struct.error):
            s.iter_unpack(b"")
        with self.assertRaises(struct.error):
            s.iter_unpack(b"12")

    def test_uninstantiable(self):
        iter_unpack_type = type(struct.Struct(">ibcp").iter_unpack(b""))
        self.assertRaises(TypeError, iter_unpack_type)

    def test_iterate(self):
        s = struct.Struct('>IB')
        b = bytes(range(1, 16))
        it = s.iter_unpack(b)
        self.assertEqual(next(it), (0x01020304, 5))
        self.assertEqual(next(it), (0x06070809, 10))
        self.assertEqual(next(it), (0x0b0c0d0e, 15))
        self.assertRaises(StopIteration, next, it)
        self.assertRaises(StopIteration, next, it)

    def test_arbitrary_buffer(self):
        s = struct.Struct('>IB')
        b = bytes(range(1, 11))
        it = s.iter_unpack(memoryview(b))
        self.assertEqual(next(it), (0x01020304, 5))
        self.assertEqual(next(it), (0x06070809, 10))
        self.assertRaises(StopIteration, next, it)
        self.assertRaises(StopIteration, next, it)

    def test_length_hint(self):
        lh = operator.length_hint
        s = struct.Struct('>IB')
        b = bytes(range(1, 16))
        it = s.iter_unpack(b)
        self.assertEqual(lh(it), 3)
        next(it)
        self.assertEqual(lh(it), 2)
        next(it)
        self.assertEqual(lh(it), 1)
        next(it)
        self.assertEqual(lh(it), 0)
        self.assertRaises(StopIteration, next, it)
        self.assertEqual(lh(it), 0)

    def test_module_func(self):
        # Sanity check for the global struct.iter_unpack()
        it = struct.iter_unpack('>IB', bytes(range(1, 11)))
        self.assertEqual(next(it), (0x01020304, 5))
        self.assertEqual(next(it), (0x06070809, 10))
        self.assertRaises(StopIteration, next, it)
        self.assertRaises(StopIteration, next, it)

    def test_half_float(self):
        _testcapi = import_helper.import_module('_testcapi')
        # Little-endian examples from:
        # http://en.wikipedia.org/wiki/Half_precision_floating-point_format
        format_bits_float__cleanRoundtrip_list = [
            (b'\x00\x3c', 1.0),
            (b'\x00\xc0', -2.0),
            (b'\xff\x7b', 65504.0), #  (max half precision)
            (b'\x00\x04', 2**-14), # ~= 6.10352 * 10**-5 (min pos normal)
            (b'\x01\x00', 2**-24), # ~= 5.96046 * 10**-8 (min pos subnormal)
            (b'\x00\x00', 0.0),
            (b'\x00\x80', -0.0),
            (b'\x00\x7c', float('+inf')),
            (b'\x00\xfc', float('-inf')),
            (b'\x55\x35', 0.333251953125), # ~= 1/3
        ]

        for le_bits, f in format_bits_float__cleanRoundtrip_list:
            be_bits = le_bits[::-1]
            self.assertEqual(f, struct.unpack('<e', le_bits)[0])
            self.assertEqual(le_bits, struct.pack('<e', f))
            self.assertEqual(f, struct.unpack('>e', be_bits)[0])
            self.assertEqual(be_bits, struct.pack('>e', f))
            if sys.byteorder == 'little':
                self.assertEqual(f, struct.unpack('e', le_bits)[0])
                self.assertEqual(le_bits, struct.pack('e', f))
            else:
                self.assertEqual(f, struct.unpack('e', be_bits)[0])
                self.assertEqual(be_bits, struct.pack('e', f))

        # Check for NaN handling:
        format_bits__nan_list = [
            ('<e', b'\x01\xfc'),
            ('<e', b'\x00\xfe'),
            ('<e', b'\xff\xff'),
            ('<e', b'\x01\x7c'),
            ('<e', b'\x00\x7e'),
            ('<e', b'\xff\x7f'),
        ]

        for formatcode, bits in format_bits__nan_list:
            self.assertTrue(math.isnan(struct.unpack('<e', bits)[0]))
            self.assertTrue(math.isnan(struct.unpack('>e', bits[::-1])[0]))

        # Check that packing produces a bit pattern representing a quiet NaN:
        # all exponent bits and the msb of the fraction should all be 1.
        if _testcapi.nan_msb_is_signaling:
            # HP PA RISC and some MIPS CPUs use 0 for quiet, see:
            # https://en.wikipedia.org/wiki/NaN#Encoding
            expected = 0x7c
        else:
            expected = 0x7e

        packed = struct.pack('<e', math.nan)
        self.assertEqual(packed[1] & 0x7e, expected)
        packed = struct.pack('<e', -math.nan)
        self.assertEqual(packed[1] & 0x7e, expected)

        # Checks for round-to-even behavior
        format_bits_float__rounding_list = [
            ('>e', b'\x00\x01', 2.0**-25 + 2.0**-35), # Rounds to minimum subnormal
            ('>e', b'\x00\x00', 2.0**-25), # Underflows to zero (nearest even mode)
            ('>e', b'\x00\x00', 2.0**-26), # Underflows to zero
            ('>e', b'\x03\xff', 2.0**-14 - 2.0**-24), # Largest subnormal.
            ('>e', b'\x03\xff', 2.0**-14 - 2.0**-25 - 2.0**-65),
            ('>e', b'\x04\x00', 2.0**-14 - 2.0**-25),
            ('>e', b'\x04\x00', 2.0**-14), # Smallest normal.
            ('>e', b'\x3c\x01', 1.0+2.0**-11 + 2.0**-16), # rounds to 1.0+2**(-10)
            ('>e', b'\x3c\x00', 1.0+2.0**-11), # rounds to 1.0 (nearest even mode)
            ('>e', b'\x3c\x00', 1.0+2.0**-12), # rounds to 1.0
            ('>e', b'\x7b\xff', 65504), # largest normal
            ('>e', b'\x7b\xff', 65519), # rounds to 65504
            ('>e', b'\x80\x01', -2.0**-25 - 2.0**-35), # Rounds to minimum subnormal
            ('>e', b'\x80\x00', -2.0**-25), # Underflows to zero (nearest even mode)
            ('>e', b'\x80\x00', -2.0**-26), # Underflows to zero
            ('>e', b'\xbc\x01', -1.0-2.0**-11 - 2.0**-16), # rounds to 1.0+2**(-10)
            ('>e', b'\xbc\x00', -1.0-2.0**-11), # rounds to 1.0 (nearest even mode)
            ('>e', b'\xbc\x00', -1.0-2.0**-12), # rounds to 1.0
            ('>e', b'\xfb\xff', -65519), # rounds to 65504
        ]

        for formatcode, bits, f in format_bits_float__rounding_list:
            self.assertEqual(bits, struct.pack(formatcode, f))

        # This overflows, and so raises an error
        format_bits_float__roundingError_list = [
            # Values that round to infinity.
            ('>e', 65520.0),
            ('>e', 65536.0),
            ('>e', 1e300),
            ('>e', -65520.0),
            ('>e', -65536.0),
            ('>e', -1e300),
            ('<e', 65520.0),
            ('<e', 65536.0),
            ('<e', 1e300),
            ('<e', -65520.0),
            ('<e', -65536.0),
            ('<e', -1e300),
        ]

        for formatcode, f in format_bits_float__roundingError_list:
            self.assertRaises(OverflowError, struct.pack, formatcode, f)

        # Double rounding
        format_bits_float__doubleRoundingError_list = [
            ('>e', b'\x67\xff', 0x1ffdffffff * 2**-26), # should be 2047, if double-rounded 64>32>16, becomes 2048
        ]

        for formatcode, bits, f in format_bits_float__doubleRoundingError_list:
            self.assertEqual(bits, struct.pack(formatcode, f))


if __name__ == '__main__':
    unittest.main()