Unpack bytes to value: unpack

The unpack template function converts bytes into a native Python value using a struct format string. This is the reverse of pack and works like Python’s struct.unpack_from function, extracting a single value from a byte sequence according to the specified format.

This function is primarily useful for IoT and low-level device communication. Many IoT devicesA device is a model representing a physical or logical unit that contains entities. send data as raw bytes that need to be interpreted according to a specific format. For example, a Bluetooth sensorSensors return information about a thing, for instance the level of water in a tank. [Learn more] might send temperature as a 16-bit big-endian integer, or an MQTT-connected microcontroller might report values in a packed binary format. The optional offset parameter lets you skip bytes at the beginning of the data, which is useful when the value you need is not at the start of the byte sequence. The format strings follow Python’s struct module syntax.

Usage

Here’s how to use this template function. Copy any example and adjust it to your setup.

{{ unpack(b"\x04\xd2", ">H") }}

1234

{{ b"\x04\xd2" | unpack(">H") }}

1234

Function signature

The signature is a technical summary of this template function. It shows the name of the function, the values (called parameters) it accepts, and what type of data each parameter expects (for example, a piece of text or a number).

Function parameters that have a = with a value after them are optional. If you leave them out, the default value shown is used automatically. Function parameters without a default are required.

unpack(
    value: bytes,
    format_string: str,
    offset: int = 0,
) -> Any | None

Function parameters

The following parameters can be provided to this function.

Using an offset

When the value you need is embedded within a larger byte sequence, use the offset parameter to skip to the right position.

{{ b"\x00\x00\x04\xd2" | unpack(">H", offset=2) }}

1234

Good to know

• Only unpacks a single value. If your format string describes multiple fields, only the first is returned. Call unpack multiple times with different offsets when you need all of them.
• The byte sequence must contain enough bytes for the format string starting at offset, otherwise the function returns None.
• Format strings follow Python’s struct module syntax, where < and > set little-endian or big-endian byte order.

Try it yourself

Ready to test this? Open Developer tools > Template, paste the example into the Template editor, and watch the result update on the right. Edit the values to see how the function adapts to your own entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this function comes up in automations and templates. Copy any example and adapt it to your setup.

Decode a BLE sensor reading

Decode a temperature value from a Bluetooth Low Energy sensor that sends data as base64-encoded big-endian bytes.

{% set raw = states("sensor.ble_raw") | base64_decode(encoding=none) %}
{{ raw | unpack(">h") / 100 }}

21.5

Decode a hex-encoded sensor value

Combine from_hex with unpack to decode a hex string containing a packed integer.

{{ "04d2" | from_hex | unpack(">H") }}

1234

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with your template and expected result, or share on our subreddit /r/homeassistant.

Related template functions

These functions work well alongside this one:

• Pack value to bytes: pack - Packs a value into bytes using a Python struct format string.

• Decode hex string to bytes: from_hex - Decodes a hexadecimal string into bytes.

• Decode from base64: base64_decode - Decodes a base64-encoded string.