Python struct.error() Examples

def main():
    """Small main program"""
    import sys, getopt
    try:
        opts, args = getopt.getopt(sys.argv[1:], 'deut')
    except getopt.error as msg:
        sys.stdout = sys.stderr
        print(msg)
        print("""usage: %s [-d|-e|-u|-t] [file|-]
        -d, -u: decode
        -e: encode (default)
        -t: encode and decode string 'Aladdin:open sesame'"""%sys.argv[0])
        sys.exit(2)
    func = encode
    for o, a in opts:
        if o == '-e': func = encode
        if o == '-d': func = decode
        if o == '-u': func = decode
        if o == '-t': test(); return
    if args and args[0] != '-':
        with open(args[0], 'rb') as f:
            func(f, sys.stdout.buffer)
    else:
        func(sys.stdin.buffer, sys.stdout.buffer) 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def _parse_hextet(cls, hextet_str):
        """Convert an IPv6 hextet string into an integer.

        Args:
            hextet_str: A string, the number to parse.

        Returns:
            The hextet as an integer.

        Raises:
            ValueError: if the input isn't strictly a hex number from
              [0..FFFF].

        """
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._HEX_DIGITS.issuperset(hextet_str):
            raise ValueError("Only hex digits permitted in %r" % hextet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(hextet_str) > 4:
            msg = "At most 4 characters permitted in %r"
            raise ValueError(msg % hextet_str)
        # Length check means we can skip checking the integer value
        return int(hextet_str, 16) 

def _process_tRNS(self, data):
        # http://www.w3.org/TR/PNG/#11tRNS
        self.trns = data
        if self.colormap:
            if not self.plte:
                warnings.warn("PLTE chunk is required before tRNS chunk.")
            else:
                if len(data) > len(self.plte)/3:
                    # Was warning, but promoted to Error as it
                    # would otherwise cause pain later on.
                    raise FormatError("tRNS chunk is too long.")
        else:
            if self.alpha:
                raise FormatError(
                  "tRNS chunk is not valid with colour type %d." %
                  self.color_type)
            try:
                self.transparent = \
                    struct.unpack("!%dH" % self.color_planes, data)
            except struct.error:
                raise FormatError("tRNS chunk has incorrect length.") 

def _handle_parsing_error(func):
    """Decorator for handling errors in raw output data."""
    @six.wraps(func)
    def wrapper(raw_data):
        msg = _('Data from Intel Node Manager %s')

        try:
            return func(raw_data)
        except (IndexError, struct.error):
            raise ironic_exception.IPMIFailure(msg % _('has wrong length.'))
        except KeyError:
            raise ironic_exception.IPMIFailure(msg % _('is corrupted.'))
        except ValueError:
            raise ironic_exception.IPMIFailure(msg % _('cannot be converted.'))

    return wrapper 

def __pack__(self):
        fmt = self.endian
        value_list = []
        for field in self._field_names_:
            fmt_ = self._field_format_[field]
            val = getattr(self, field)
            if isinstance(fmt_, StructArray):
                value_list.extend([
                    getattr(struct_, field)
                    for struct_ in fmt_.structure_list
                    for field in struct_._field_names_
                ])
            elif isinstance(fmt_, basestring) and (fmt_.startswith('BBB') or fmt_.startswith('bbb')):
                value_list.extend([(val >> i & 0xFF) for i in [x for x in range(0, len(fmt_) * 8, 8)]])
            else:    
                try:
                    value_list.append(val.encode('ascii', 'ignore'))
                except AttributeError:
                    value_list.append(val)
            fmt += str(len(val)) + 's' if fmt_ == 'variable' else fmt_.get_struct() if isinstance(fmt_, StructArray) else fmt_
        try:
            return struct.pack(fmt, *value_list)
        except struct.error as exc:
            raise_from(PackError("Unable to pack structure"), exc) 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def _parse_hextet(cls, hextet_str):
        """Convert an IPv6 hextet string into an integer.

        Args:
            hextet_str: A string, the number to parse.

        Returns:
            The hextet as an integer.

        Raises:
            ValueError: if the input isn't strictly a hex number from
              [0..FFFF].

        """
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._HEX_DIGITS.issuperset(hextet_str):
            raise ValueError("Only hex digits permitted in %r" % hextet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(hextet_str) > 4:
            msg = "At most 4 characters permitted in %r"
            raise ValueError(msg % hextet_str)
        # Length check means we can skip checking the integer value
        return int(hextet_str, 16) 

def __init__(self, file, align=True, bigendian=True, inclheader=False):
        import struct
        self.closed = False
        self.align = align      # whether to align to word (2-byte) boundaries
        if bigendian:
            strflag = '>'
        else:
            strflag = '<'
        self.file = file
        self.chunkname = file.read(4)
        if len(self.chunkname) < 4:
            raise EOFError
        try:
            self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
        except struct.error:
            raise EOFError
        if inclheader:
            self.chunksize = self.chunksize - 8 # subtract header
        self.size_read = 0
        try:
            self.offset = self.file.tell()
        except (AttributeError, IOError):
            self.seekable = False
        else:
            self.seekable = True 

def seek(self, pos, whence=0):
        """Seek to specified position into the chunk.
        Default position is 0 (start of chunk).
        If the file is not seekable, this will result in an error.
        """

        if self.closed:
            raise ValueError, "I/O operation on closed file"
        if not self.seekable:
            raise IOError, "cannot seek"
        if whence == 1:
            pos = pos + self.size_read
        elif whence == 2:
            pos = pos + self.chunksize
        if pos < 0 or pos > self.chunksize:
            raise RuntimeError
        self.file.seek(self.offset + pos, 0)
        self.size_read = pos 

def close(self,

              remove=os.unlink,error=os.error):

        if self.pipe:
            rc = self.pipe.close()
        else:
            rc = 255
        if self.tmpfile:
            try:
                remove(self.tmpfile)
            except error:
                pass
        return rc

    # Alias 

def _node(default=''):

    """ Helper to determine the node name of this machine.
    """
    try:
        import socket
    except ImportError:
        # No sockets...
        return default
    try:
        return socket.gethostname()
    except socket.error:
        # Still not working...
        return default

# os.path.abspath is new in Python 1.5.2: 

def _iesubelmsmtreqstasta_(s,sid):
    """ :returns: parsed subelement of type sta request for sta counters in msmt request """
    ret = s
    if sid == std.EID_MSMT_REQ_SUBELEMENT_STA_RPT:
        # Std Fig. 8-117
        cnt,to,t = struct.unpack_from('=I2H',s)
        ts = s[8:]
        ret = {'msmt-cnt':cnt,
               'trigger-timeout':to,
               'sta-cntr-trigger-cond':_stacntrtriggerconds_(t),
               'thresholds':{}}

        # optional count fields are 4-bytes assuming they are appending in order
        for thresh in ['fail','fcs-error','mult-retry','dup','rts-fail','ack-fail','retry-cnt']:
            if ret['sta-cntr-trigger-cond'][thresh]:
                ret['thresholds'][thresh] = struct.unpack_from('=I',ts)[0]
                ts = ts[4:]
    elif sid == std.EID_MSMT_REQ_SUBELEMENT_STA_VEND:
        ret = _parseie_(std.EID_VEND_SPEC,s)
    return ret

# STA Counter Trigger Conditions Std Fig. 8-118 

def ampduflags_get(mn,f):
    try:
        return bitmask_get(_AMPDU_FLAGS_,mn,f)
    except KeyError:
        raise error("Invalid A-MPDU flag {0}".format(f))
        
# --> VHT Known <-- http://www.radiotap.org/defined-fields/VHT
# stbc STBC known
# txop TXOP_PS_NOT_ALLOWED known
# gi Guard Interval
# short Short GI NYSI disambiguation known
# ldpc LDPC extra OFDM symbol known
# beam Beamformed known
# bw Bandwidth known
# gid Group ID known
# paid Partial AID known 

def vhtknown_get(mn,f):
    try:
        return bitmask_get(_VHT_KNOWN_,mn,f)
    except KeyError:
        raise error("Invalid VHT Known field {0}".format(f))

# --> VHT Flags <-- http://www.radiotap.org/defined-fields/VHT
# stbc Space-Time Block Coding (Set to 0 if no spatial streams of any user has STBC.
#                               Set to 1 if all spatial streams of all users have STBC.
# txop TXOP_PS_NOT_ALLOWED known Valid only for AP transmitters. Set to 0 if STAs 
#      may doze during TXOP. Set to 1 if STAs may not doze during TXOP or trans
#      is non-AP.
# gi Guard Interval Set to 0 for long GI. Set to 1 for short GI.
# short Short GI NYSI disambiguation Valid only if short GI is used. Set to 0 if 
#       NSYM mod 10 != 9 or short GI not used. Set to 1 if NSYM mod 10 = 9.
# ldpc LDPC extra OFDM symbol Set to 1 if >= 1 users are using LDPC and the encoding 
#      process resulted in extra OFDM symbol(s). Set to 0 otherwise
# beam Beamformed Valid for SU PPDUs only 

def close(self):
        """
        Closes the file pointer, if possible.

        This operation will destroy the image core and release its memory.
        The image data will be unusable afterward.

        This function is only required to close images that have not
        had their file read and closed by the
        :py:meth:`~PIL.Image.Image.load` method.
        """
        try:
            self.fp.close()
        except Exception as msg:
            logger.debug("Error closing: %s", msg)

        # Instead of simply setting to None, we're setting up a
        # deferred error that will better explain that the core image
        # object is gone.
        self.im = deferred_error(ValueError("Operation on closed image")) 

def getData(self):
		"""Assemble the data for this writer/table, without subtables."""
		items = list(self.items)  # make a shallow copy
		pos = self.pos
		numItems = len(items)
		for i in range(numItems):
			item = items[i]

			if hasattr(item, "getData"):
				if item.longOffset:
					items[i] = packULong(item.pos - pos)
				else:
					try:
						items[i] = packUShort(item.pos - pos)
					except struct.error:
						# provide data to fix overflow problem.
						overflowErrorRecord = self.getOverflowErrorRecord(item)

						raise OTLOffsetOverflowError(overflowErrorRecord)

		return bytesjoin(items) 

def _bson_to_dict(data, opts):
    """Decode a BSON string to document_class."""
    try:
        obj_size = _UNPACK_INT(data[:4])[0]
    except struct.error as exc:
        raise InvalidBSON(str(exc))
    if obj_size != len(data):
        raise InvalidBSON("invalid object size")
    if data[obj_size - 1:obj_size] != b"\x00":
        raise InvalidBSON("bad eoo")
    try:
        if _raw_document_class(opts.document_class):
            return opts.document_class(data, opts)
        return _elements_to_dict(data, 4, obj_size - 1, opts)
    except InvalidBSON:
        raise
    except Exception:
        # Change exception type to InvalidBSON but preserve traceback.
        _, exc_value, exc_tb = sys.exc_info()
        reraise(InvalidBSON, exc_value, exc_tb) 

def crc(self, cid, data):
        "Read and verify checksum"

        # Skip CRC checks for ancillary chunks if allowed to load truncated images
        # 5th byte of first char is 1 [specs, section 5.4]
        if ImageFile.LOAD_TRUNCATED_IMAGES and (i8(cid[0]) >> 5 & 1):
            self.crc_skip(cid, data)
            return

        try:
            crc1 = Image.core.crc32(data, Image.core.crc32(cid))
            crc2 = i16(self.fp.read(2)), i16(self.fp.read(2))
            if crc1 != crc2:
                raise SyntaxError("broken PNG file (bad header checksum in %r)"
                                  % cid)
        except struct.error:
            raise SyntaxError("broken PNG file (incomplete checksum in %r)"
                              % cid) 

def close(self):
        """
        Closes the file pointer, if possible.

        This operation will destroy the image core and release its memory.
        The image data will be unusable afterward.

        This function is only required to close images that have not
        had their file read and closed by the
        :py:meth:`~PIL.Image.Image.load` method.
        """
        try:
            self.fp.close()
            self.fp = None
        except Exception as msg:
            logger.debug("Error closing: %s", msg)

        if getattr(self, 'map', None):
            self.map = None
    
        # Instead of simply setting to None, we're setting up a
        # deferred error that will better explain that the core image
        # object is gone.
        self.im = deferred_error(ValueError("Operation on closed image")) 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def _parse_hextet(cls, hextet_str):
        """Convert an IPv6 hextet string into an integer.

        Args:
            hextet_str: A string, the number to parse.

        Returns:
            The hextet as an integer.

        Raises:
            ValueError: if the input isn't strictly a hex number from
              [0..FFFF].

        """
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._HEX_DIGITS.issuperset(hextet_str):
            raise ValueError("Only hex digits permitted in %r" % hextet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(hextet_str) > 4:
            msg = "At most 4 characters permitted in %r"
            raise ValueError(msg % hextet_str)
        # Length check means we can skip checking the integer value
        return int(hextet_str, 16) 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def _parse_hextet(cls, hextet_str):
        """Convert an IPv6 hextet string into an integer.

        Args:
            hextet_str: A string, the number to parse.

        Returns:
            The hextet as an integer.

        Raises:
            ValueError: if the input isn't strictly a hex number from
              [0..FFFF].

        """
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._HEX_DIGITS.issuperset(hextet_str):
            raise ValueError("Only hex digits permitted in %r" % hextet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(hextet_str) > 4:
            msg = "At most 4 characters permitted in %r"
            raise ValueError(msg % hextet_str)
        # Length check means we can skip checking the integer value
        return int(hextet_str, 16) 

def _read_elf_file(self, f):
        # read the ELF file header
        LEN_FILE_HEADER = 0x34
        try:
            (ident,_type,machine,_version,
             self.entrypoint,_phoff,shoff,_flags,
             _ehsize, _phentsize,_phnum,_shentsize,
             _shnum,shstrndx) = struct.unpack("<16sHHLLLLLHHHHHH", f.read(LEN_FILE_HEADER))
        except struct.error as e:
            raise FatalError("Failed to read a valid ELF header from %s: %s" % (self.name, e))

        if byte(ident, 0) != 0x7f or ident[1:4] != b'ELF':
            raise FatalError("%s has invalid ELF magic header" % self.name)
        if machine != 0x5e:
            raise FatalError("%s does not appear to be an Xtensa ELF file. e_machine=%04x" % (self.name, machine))
        self._read_sections(f, shoff, shstrndx) 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def _parse_hextet(cls, hextet_str):
        """Convert an IPv6 hextet string into an integer.

        Args:
            hextet_str: A string, the number to parse.

        Returns:
            The hextet as an integer.

        Raises:
            ValueError: if the input isn't strictly a hex number from
              [0..FFFF].

        """
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._HEX_DIGITS.issuperset(hextet_str):
            raise ValueError("Only hex digits permitted in %r" % hextet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(hextet_str) > 4:
            msg = "At most 4 characters permitted in %r"
            raise ValueError(msg % hextet_str)
        # Length check means we can skip checking the integer value
        return int(hextet_str, 16) 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def _parse_hextet(cls, hextet_str):
        """Convert an IPv6 hextet string into an integer.

        Args:
            hextet_str: A string, the number to parse.

        Returns:
            The hextet as an integer.

        Raises:
            ValueError: if the input isn't strictly a hex number from
              [0..FFFF].

        """
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._HEX_DIGITS.issuperset(hextet_str):
            raise ValueError("Only hex digits permitted in %r" % hextet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(hextet_str) > 4:
            msg = "At most 4 characters permitted in %r"
            raise ValueError(msg % hextet_str)
        # Length check means we can skip checking the integer value
        return int(hextet_str, 16) 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def _parse_hextet(cls, hextet_str):
        """Convert an IPv6 hextet string into an integer.

        Args:
            hextet_str: A string, the number to parse.

        Returns:
            The hextet as an integer.

        Raises:
            ValueError: if the input isn't strictly a hex number from
              [0..FFFF].

        """
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._HEX_DIGITS.issuperset(hextet_str):
            raise ValueError("Only hex digits permitted in %r" % hextet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(hextet_str) > 4:
            msg = "At most 4 characters permitted in %r"
            raise ValueError(msg % hextet_str)
        # Length check means we can skip checking the integer value
        return int(hextet_str, 16) 

def crc(self, cid, data):
        "Read and verify checksum"

        # Skip CRC checks for ancillary chunks if allowed to load truncated images
        # 5th byte of first char is 1 [specs, section 5.4]
        if ImageFile.LOAD_TRUNCATED_IMAGES and (i8(cid[0]) >> 5 & 1):
            self.crc_skip(cid, data)
            return

        try:
            crc1 = Image.core.crc32(data, Image.core.crc32(cid))
            crc2 = i16(self.fp.read(2)), i16(self.fp.read(2))
            if crc1 != crc2:
                raise SyntaxError("broken PNG file (bad header checksum in %r)"
                                  % cid)
        except struct.error:
            raise SyntaxError("broken PNG file (incomplete checksum in %r)"
                              % cid) 

def close(self):
        """
        Closes the file pointer, if possible.

        This operation will destroy the image core and release its memory.
        The image data will be unusable afterward.

        This function is only required to close images that have not
        had their file read and closed by the
        :py:meth:`~PIL.Image.Image.load` method.
        """
        try:
            self.fp.close()
            self.fp = None
        except Exception as msg:
            logger.debug("Error closing: %s", msg)

        if getattr(self, 'map', None):
            self.map = None

        # Instead of simply setting to None, we're setting up a
        # deferred error that will better explain that the core image
        # object is gone.
        self.im = deferred_error(ValueError("Operation on closed image")) 

def _process_tRNS(self, data):
        # http://www.w3.org/TR/PNG/#11tRNS
        self.trns = data
        if self.colormap:
            if not self.plte:
                warnings.warn("PLTE chunk is required before tRNS chunk.")
            else:
                if len(data) > len(self.plte)/3:
                    # Was warning, but promoted to Error as it
                    # would otherwise cause pain later on.
                    raise FormatError("tRNS chunk is too long.")
        else:
            if self.alpha:
                raise FormatError(
                  "tRNS chunk is not valid with colour type %d." %
                  self.color_type)
            try:
                self.transparent = \
                    struct.unpack("!%dH" % self.color_planes, data)
            except struct.error:
                raise FormatError("tRNS chunk has incorrect length.") 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def _parse_hextet(cls, hextet_str):
        """Convert an IPv6 hextet string into an integer.

        Args:
            hextet_str: A string, the number to parse.

        Returns:
            The hextet as an integer.

        Raises:
            ValueError: if the input isn't strictly a hex number from
              [0..FFFF].

        """
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._HEX_DIGITS.issuperset(hextet_str):
            raise ValueError("Only hex digits permitted in %r" % hextet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(hextet_str) > 4:
            msg = "At most 4 characters permitted in %r"
            raise ValueError(msg % hextet_str)
        # Length check means we can skip checking the integer value
        return int(hextet_str, 16) 

def v4_int_to_packed(address):
    """Represent an address as 4 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv4 IP address.

    Returns:
        The integer address packed as 4 bytes in network (big-endian) order.

    Raises:
        ValueError: If the integer is negative or too large to be an
          IPv4 IP address.

    """
    try:
        return _compat_to_bytes(address, 4, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv4") 

def __init__(self, address):

        """
        Args:
            address: A string or integer representing the IP
              '192.168.1.1'

              Additionally, an integer can be passed, so
              IPv4Address('192.168.1.1') == IPv4Address(3232235777).
              or, more generally
              IPv4Address(int(IPv4Address('192.168.1.1'))) ==
                IPv4Address('192.168.1.1')

        Raises:
            AddressValueError: If ipaddr isn't a valid IPv4 address.

        """
        _BaseV4.__init__(self, address)

        # Efficient constructor from integer.
        if isinstance(address, (int, long)):
            self._ip = address
            if address < 0 or address > self._ALL_ONES:
                raise AddressValueError(address)
            return

        # Constructing from a packed address
        if isinstance(address, Bytes):
            try:
                self._ip, = struct.unpack('!I', address)
            except struct.error:
                raise AddressValueError(address)  # Wrong length.
            return

        # Assume input argument to be string or any object representation
        # which converts into a formatted IP string.
        addr_str = str(address)
        self._ip = self._ip_int_from_string(addr_str) 

def _compat_to_bytes(intval, length, endianess):
    assert isinstance(intval, _compat_int_types)
    assert endianess == 'big'
    if length == 4:
        if intval < 0 or intval >= 2 ** 32:
            raise struct.error("integer out of range for 'I' format code")
        return struct.pack(b'!I', intval)
    elif length == 16:
        if intval < 0 or intval >= 2 ** 128:
            raise struct.error("integer out of range for 'QQ' format code")
        return struct.pack(b'!QQ', intval >> 64, intval & 0xffffffffffffffff)
    else:
        raise NotImplementedError() 

def v6_int_to_packed(address):
    """Represent an address as 16 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv6 IP address.

    Returns:
        The integer address packed as 16 bytes in network (big-endian) order.

    """
    try:
        return _compat_to_bytes(address, 16, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv6") 

def _parse_octet(cls, octet_str):
        """Convert a decimal octet into an integer.

        Args:
            octet_str: A string, the number to parse.

        Returns:
            The octet as an integer.

        Raises:
            ValueError: if the octet isn't strictly a decimal from [0..255].

        """
        if not octet_str:
            raise ValueError("Empty octet not permitted")
        # Whitelist the characters, since int() allows a lot of bizarre stuff.
        if not cls._DECIMAL_DIGITS.issuperset(octet_str):
            msg = "Only decimal digits permitted in %r"
            raise ValueError(msg % octet_str)
        # We do the length check second, since the invalid character error
        # is likely to be more informative for the user
        if len(octet_str) > 3:
            msg = "At most 3 characters permitted in %r"
            raise ValueError(msg % octet_str)
        # Convert to integer (we know digits are legal)
        octet_int = int(octet_str, 10)
        # Any octets that look like they *might* be written in octal,
        # and which don't look exactly the same in both octal and
        # decimal are rejected as ambiguous
        if octet_int > 7 and octet_str[0] == '0':
            msg = "Ambiguous (octal/decimal) value in %r not permitted"
            raise ValueError(msg % octet_str)
        if octet_int > 255:
            raise ValueError("Octet %d (> 255) not permitted" % octet_int)
        return octet_int 

def iterstraight(self, raw):
        """Iterator that undoes the effect of filtering, and yields
        each row in serialised format (as a sequence of bytes).
        Assumes input is straightlaced.  `raw` should be an iterable
        that yields the raw bytes in chunks of arbitrary size.
        """

        # length of row, in bytes
        rb = self.row_bytes
        a = array('B')
        # The previous (reconstructed) scanline.  None indicates first
        # line of image.
        recon = None
        for some in raw:
            a.extend(some)
            while len(a) >= rb + 1:
                filter_type = a[0]
                scanline = a[1:rb+1]
                del a[:rb+1]
                recon = self.undo_filter(filter_type, scanline, recon)
                yield recon
        if len(a) != 0:
            # :file:format We get here with a file format error:
            # when the available bytes (after decompressing) do not
            # pack into exact rows.
            raise FormatError(
              'Wrong size for decompressed IDAT chunk.')
        assert len(a) == 0 

def _process_bKGD(self, data):
        try:
            if self.colormap:
                if not self.plte:
                    warnings.warn(
                      "PLTE chunk is required before bKGD chunk.")
                self.background = struct.unpack('B', data)
            else:
                self.background = struct.unpack("!%dH" % self.color_planes,
                  data)
        except struct.error:
            raise FormatError("bKGD chunk has incorrect length.") 

def _process_gAMA(self, data):
        try:
            self.gamma = struct.unpack("!L", data)[0] / 100000.0
        except struct.error:
            raise FormatError("gAMA chunk has incorrect length.") 

def __unpack__(self, type_, buf, _size=None):
        fmt = self.endian + type_
        size = struct.calcsize(fmt) if _size is None else _size
        try:
            unpacked = struct.unpack(fmt, buf[:size]), buf[size:]
        except struct.error as exc:
            raise_from(UnpackError("Unable to unpack structure"), exc)
        else:
            return unpacked 

def _compat_to_bytes(intval, length, endianess):
    assert isinstance(intval, _compat_int_types)
    assert endianess == 'big'
    if length == 4:
        if intval < 0 or intval >= 2 ** 32:
            raise struct.error("integer out of range for 'I' format code")
        return struct.pack(b'!I', intval)
    elif length == 16:
        if intval < 0 or intval >= 2 ** 128:
            raise struct.error("integer out of range for 'QQ' format code")
        return struct.pack(b'!QQ', intval >> 64, intval & 0xffffffffffffffff)
    else:
        raise NotImplementedError() 

def v6_int_to_packed(address):
    """Represent an address as 16 packed bytes in network (big-endian) order.

    Args:
        address: An integer representation of an IPv6 IP address.

    Returns:
        The integer address packed as 16 bytes in network (big-endian) order.

    """
    try:
        return _compat_to_bytes(address, 16, 'big')
    except (struct.error, OverflowError):
        raise ValueError("Address negative or too large for IPv6")