Package: cstruct
Python-CStructC-style structs for PythonConvert C struct/union definitions into Python classes with methods for
serializing/deserializing.The usage is very simple: create a class subclassingcstruct.MemCStructand add a C struct/union definition as a string in the__def__field.The C struct/union definition is parsed at runtime and the struct format string
is generated. The class offers the methodunpackfor deserializing
an array of bytes into a Python object and the methodpackfor
serializing the values into an array of bytes.Installpip install cstructExamplesRead the DOS-type (MBR) partition tablePrint information about logged usesFlexible Array Member (FAM)libc integration (using ctypes)FeaturesStructsStruct definition subclassingcstruct.MemCStruct. Methods can access stuct values as instance variables.classPosition(cstruct.MemCStruct):__def__="""struct {unsigned char head;unsigned char sector;unsigned char cyl;}"""@propertydeflba(self):return(self.cyl*16+self.head)*63+(self.sector-1)pos=Position(cyl=15,head=15,sector=63)print(f"head:{pos.head}sector:{pos.sector}cyl:{pos.cyl}lba:{pos.lba}")Struct definition usingcstruct.parse.Partition=cstruct.parse("""#define ACTIVE_FLAG         0x80struct Partition {unsigned char status;       /* 0x80 - active */struct Position start;unsigned char partition_type;struct Position end;unsigned int start_sect;    /* starting sector counting from 0 */unsigned int sectors;       /* nr of sectors in partition */}""")part=Partition()part.status=cstruct.getdef('ACTIVE_FLAG')UnionsUnion definition subclassingcstruct.MemCStruct.classData(cstruct.MemCStruct):__def__="""union {int integer;float real;}"""data=Data()data.integer=2data.real=3assertdata.integer!=2EnumsEnum definition subclassingcstruct.CEnum.classHtmlFont(cstruct.CEnum):__size__=2__def__="""#define NONE         0enum htmlfont {HTMLFONT_NONE = NONE,HTMLFONT_BOLD,HTMLFONT_ITALIC}"""assertHtmlFont.HTMLFONT_NONE==0assertHtmlFont.HTMLFONT_BOLD==1assertHtmlFont.HTMLFONT_ITALIC==2Different enum styles are supported in struct/union definitions.enumType_Aa;// externally defined using CEnumenumType_B{A,B,C}b;enum{A,B,C}c;enumType_D:short{A,B,C}d;// specify the underlying typeenumDirection{left='l',right='r'};Nested structs/unionsNested stucts and unions are supported, both named and anonymous.classPacket(cstruct.MemCStruct):__def__="""struct Packet {uint8_t packetLength;union {struct {uint16_t field1;uint16_t field2;uint16_t field3;} format1;struct {double value1;double value2;} format2;};};"""Byte Order, Size, and PaddingSuported byte orders:cstruct.LITTLE_ENDIAN- Little endian byte order, standard size, no paddingcstruct.BIG_ENDIAN- Big endian byte order, standard size, no paddingcstruct.NATIVE_ORDER- Native byte order, native size, paddingclassNative(cstruct.MemCStruct):__byte_order__=cstruct.NATIVE_ORDER__def__="""struct {long p;char c;long x;}"""Flexible Array MemberclassPkg(cstruct.MemCStruct):__byte_order__=cstruct.LITTLE_ENDIAN__def__="""struct {uint16_t cmd;uint16_t length;uint8_t data[];}"""pkg=Pkg()pkg.length=4pkg.data=[10,20,30,40]Pack and UnpackA code example illustrating how to usepackto pack a structure into binary form.classPosition(cstruct.MemCStruct):__byte_order__=cstruct.LITTLE_ENDIAN__def__="""struct {unsigned char head;unsigned char sector;unsigned char cyl;}"""pos=Position(head=10,sector=20,cyl=3)packed=pos.pack()Binary representation can be converted into structure usingunpack.pos1 = Position()
pos1.unpack(packed)
assert pos1.head == 10
assert pos1.sector == 20
assert pos1.cyl == 3Define, Sizeof, and EvalDefinitions in Struct declaration:classPacket(cstruct.MemCStruct):__byte_order__=cstruct.LITTLE_ENDIAN__def__="""#define MaxPacket 20struct Packet {uint8_t bytes[MaxPacket];}"""Parse C definitions:cstruct.parse("""#define A1  10#define A2  10 + A1#define A3  30""")assertcstruct.getdef("A1")==10assertcstruct.getdef('A2')==20Get structure size:cstruct.sizeof(Partition)Evaluate C expression usingc_eval:cstruct.c_eval("A1 / 10")cstruct.c_eval("((A10 < 6) || (A10>10))")C expressions are automatically evaluated during structure definitions:classMBR(cstruct.MemCStruct):__byte_order__=cstruct.LITTLE_ENDIAN__def__="""#define MBR_SIZE                    512#define MBR_DISK_SIGNATURE_SIZE       4#define MBR_USUALY_NULLS_SIZE         2#define MBR_SIGNATURE_SIZE            2#define MBR_BOOT_SIGNATURE       0xaa55#define MBR_PARTITIONS_NUM            4#define MBR_PARTITIONS_SIZE  (sizeof(Partition) * MBR_PARTITIONS_NUM)#define MBR_UNUSED_SIZE      (MBR_SIZE - MBR_DISK_SIGNATURE_SIZE - MBR_USUALY_NULLS_SIZE - MBR_PARTITIONS_SIZE - MBR_SIGNATURE_SIZE)struct {char unused[MBR_UNUSED_SIZE];unsigned char disk_signature[MBR_DISK_SIGNATURE_SIZE];unsigned char usualy_nulls[MBR_USUALY_NULLS_SIZE];struct Partition partitions[MBR_PARTITIONS_NUM];uint16 signature;}"""Ispect memoryTheinspectmethods displays memory contents in hexadecimal.print(mbr.inspect())Output example:00000000  eb 48 90 00 00 00 00 00  00 00 00 00 00 00 00 00  |.H..............|
00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 03 02  |................|
00000040  ff 00 00 80 61 cb 04 00  00 08 fa 80 ca 80 ea 53  |....a..........S|
00000050  7c 00 00 31 c0 8e d8 8e  d0 bc 00 20 fb a0 40 7c  ||..1....... ..@||
00000060  3c ff 74 02 88 c2 52 be  79 7d e8 34 01 f6 c2 80  |<.t...R.y}.4....|
00000070  74 54 b4 41 bb aa 55 cd  13 5a 52 72 49 81 fb 55  |tT.A..U..ZRrI..U|
00000080  aa 75 43 a0 41 7c 84 c0  75 05 83 e1 01 74 37 66  |.uC.A|..u....t7f|
00000090  8b 4c 10 be 05 7c c6 44  ff 01 66 8b 1e 44 7c c7  |.L...|.D..f..D|.|
000000a0  04 10 00 c7 44 02 01 00  66 89 5c 08 c7 44 06 00  |....D...f.\..D..|
000000b0  70 66 31 c0 89 44 04 66  89 44 0c b4 42 cd 13 72  |pf1..D.f.D..B..r|
000000c0  05 bb 00 70 eb 7d b4 08  cd 13 73 0a f6 c2 80 0f  |...p.}....s.....|
000000d0  84 f0 00 e9 8d 00 be 05  7c c6 44 ff 00 66 31 c0  |........|.D..f1.|
000000e0  88 f0 40 66 89 44 04 31  d2 88 ca c1 e2 02 88 e8  |..@f.D.1........|
000000f0  88 f4 40 89 44 08 31 c0  88 d0 c0 e8 02 66 89 04  |..@.D.1......f..|
00000100  66 a1 44 7c 66 31 d2 66  f7 34 88 54 0a 66 31 d2  |f.D|f1.f.4.T.f1.|
00000110  66 f7 74 04 88 54 0b 89  44 0c 3b 44 08 7d 3c 8a  |f.t..T..D.;D.}<.|
00000120  54 0d c0 e2 06 8a 4c 0a  fe c1 08 d1 8a 6c 0c 5a  |T.....L......l.Z|
00000130  8a 74 0b bb 00 70 8e c3  31 db b8 01 02 cd 13 72  |.t...p..1......r|
00000140  2a 8c c3 8e 06 48 7c 60  1e b9 00 01 8e db 31 f6  |*....H|`......1.|
00000150  31 ff fc f3 a5 1f 61 ff  26 42 7c be 7f 7d e8 40  |1.....a.&B|..}.@|
00000160  00 eb 0e be 84 7d e8 38  00 eb 06 be 8e 7d e8 30  |.....}.8.....}.0|
00000170  00 be 93 7d e8 2a 00 eb  fe 47 52 55 42 20 00 47  |...}.*...GRUB .G|
00000180  65 6f 6d 00 48 61 72 64  20 44 69 73 6b 00 52 65  |eom.Hard Disk.Re|
00000190  61 64 00 20 45 72 72 6f  72 00 bb 01 00 b4 0e cd  |ad. Error.......|
000001a0  10 ac 3c 00 75 f4 c3 00  00 00 00 00 00 00 00 00  |..<.u...........|
000001b0  00 00 00 00 00 00 00 00  40 e2 01 00 00 00 80 00  |........@.......|
000001c0  02 00 83 fe 3f 86 01 00  00 00 c6 17 21 00 00 00  |....?.......!...|
000001d0  01 87 8e fe ff ff c7 17  21 00 4d d3 de 00 00 00  |........!.M.....|
000001e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 55 aa  |..............U.|LinksC/C++ reference