struct – pack and unpack primitive data types

This module performs conversions between Python values and C-style structs represented as Python bytes objects, using format strings to describe the layout of the data.

The following byte orders are supported:

Character	Byte order	Size	Alignment
@	native	native	native
<	little-endian	standard	none
>	big-endian	standard	none
!	network (= big-endian)	standard	none

The following data types are supported:

Format	C Type	Python type	Standard size
b	signed char	integer	1
B	unsigned char	integer	1
h	short	integer	2
H	unsigned short	integer	2
i	int	integer (1)	4
I	unsigned int	integer (1)	4
l	long	integer (1)	4
L	unsigned long	integer (1)	4
q	long long	integer (1)	8
Q	unsigned long long	integer (1)	8
e	n/a (half-float)	float (2)	2
f	float	float (2)	4
d	double	float (2)	8
s	char[]	bytes
P	void *	integer

1. Requires long support when used with values larger than 30 bits.

2. Requires floating point support.

Difference to CPython

Whitespace is not supported in format strings.

Functions

struct.calcsize(fmt: str) → int

Return the number of bytes needed to store the given fmt.

struct.pack(fmt: str, *values: Any) → bytes

Pack the values according to the format string fmt. The return value is a bytes object encoding the values.

struct.pack_into(fmt: str, buffer: Any, offset: int, *values: Any) → None

Pack the values according to the format string fmt into a buffer starting at offset. offset may be negative to count from the end of buffer.

struct.unpack(fmt: str, data: bytes) → Tuple

Unpack from the data according to the format string fmt. The return value is a tuple of the unpacked values.

struct.unpack_from(fmt: str, data: bytes, offset: int = 0, /) → Tuple

Unpack from the data starting at offset according to the format string fmt. offset may be negative to count from the end of data. The return value is a tuple of the unpacked values.