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struct – pack and unpack primitive data types

This module implements a subset of the corresponding CPython module, as described below. For more information, refer to the original CPython documentation: struct.

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
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)

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

struct.pack(fmt, v1, v2, ...)

Pack the values v1, v2, … according to the format string fmt. The return value is a bytes object encoding the values.

struct.pack_into(fmt, buffer, offset, v1, v2, ...)

Pack the values v1, v2, … 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, data)

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

struct.unpack_from(fmt, data, offset=0, /)

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.