unpack

Syntax

unpack(format, buf)

Details

Unpack from the buf according to the format string specified by format. The result is a tuple with the unpacked data even if it contains exactly one item.

Parameters

format is a format string.

A format character may be preceded by an integral repeat count. For example, the format string '4h' means exactly the same as 'hhhh'.
Whitespace characters between formats are ignored; a count and its format must not contain whitespace though.
For the 's' format character, the count is interpreted as the length of the bytes, not a repeat count like for the other format characters; for example, '10s' means a single 10-byte string, while '10c' means 10 characters. If a count is not given, it defaults to 1. The string is truncated or padded with null bytes as appropriate to make it fit.

buf is a bytes object of STRING or BLOB type. The size of buf in bytes must match the size required by the format.

Returns

It returns a tuple with the unpacked data.

Examples

res = pack("N",1);
res1 = unpack("N", res);
print(res1)
// output: (1)

res = pack("3s i", `123, 3)
res1 = unpack("3s i",  res);
print(res1)
// output: ("123",3)

res = pack("3s i", `123, 3)
res2 = unpack("3s i",  blob(res));
print(res2)
// output: ("123",3)

Related function: pack

Appendix

Format Characters

Format mapping:


Format	C Type	Python Type	DolphinDB Type	Range
x	pad byte	no value	VOID
c	char	bytes of length 1	CHAR	-27 +1~27 -1
b	signed char	integer	LONG	-27 ~27 -1
B	unsigned char	integer	LONG	0~28 -1
?	_Bool	bool	LONG	-263 ~263 -1
h	short	integer	LONG	-215 ~215 -1
H	unsigned short	integer	LONG	0~216 -1
i	int	integer	LONG	-231 ~231 -1
I	unsigned int	integer	LONG	0~232 -1
l	long	integer	LONG	-231~231 -1
L	unsigned long	integer	LONG	0~232 -1
q	long long	integer	LONG	-263 ~263 -1
Q	unsigned long long	integer	LONG	0~263 -1
n	ssize_t	integer	LONG	-263 ~263 -1
N	size_t	integer	LONG	0~263 -1
f	float	float	LONG	-3.40E+38 ~ +3.40E+38
d	double	float	LONG	-1.79E+308 ~ +1.79E+308
s	char[]	bytes	STRING
p	char[]	bytes	STRING
P	void*	integer	LONG	-263 ~263 -1

Byte Order, Size, and Alignment


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

The first character of the format string can be used to indicate the byte order, size and alignment of the packed data, see "Appendix: Byte Order, Size and Alignment". If the first character is not one of these characters, '@' is assumed.