# `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.

Language and External Links

Language
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External links
  openmv.io
  forums.openmv.io
  github.com/openmv/openmv
  micropython.org
  forum.micropython.org
  github.com/micropython/micropython