UTTLV - Python TLV (Tag-Length-Value) Library

0.7.1 verified Fri May 01 auth: no python

A Python library for encoding and decoding TLV (Tag-Length-Value) objects. Supports custom tag definitions, nested TLV structures, and iterator access. Current version 0.7.1, maintained on GitHub.

pip install uttlv

Common errors

error TypeError: 'Tlv' object does not support item assignment ↓

cause Attempting to assign to a Tlv object that has not been initialized properly or using a non-integer tag.

fix

Ensure you have created a Tlv instance: tlv = Tlv() and use integer tags: tlv[0x01] = b'data'

error ValueError: Invalid tag length size ↓

cause The tag_len_sizes parameter is not correctly specified or the encoded TLV uses lengths outside the defined sizes.

fix

Define tag_len_sizes as a dict mapping tag ranges to (tag_bytes, length_bytes). Default is {0x00: (1,1)}. See docs for custom sizes.

error Exception: TLV parse error: unknown tag ↓

cause Decoding TLV with tags not present in the current Tlv instance's tag registry.

fix

Use the same Tlv instance or configure the decoder with expected tags via tag_len_sizes or nested_tag_config_map.

Warnings

breaking In v0.7.0, the 'nested_tag_config_map' parameter was added to Tlv constructor, changing the signature. Code using positional arguments for 'tag_len_sizes' may break. ↓

fix Update constructor calls to use keyword arguments: Tlv(tag_len_sizes=...) if needed.

gotcha Tag values must be integers; assigning non-integer keys will raise TypeError. ↓

fix Always use integer tag values, e.g., tlv[0x01] = b'...'.

gotcha When decoding, from_bytes() expects bytes, not hex string. Common mistake is passing a hex string directly. ↓

fix Convert hex string to bytes first: tlv.from_bytes(bytes.fromhex('010203'))

Imports

Tlv
```
from uttlv import Tlv
```

Quickstart

Create a TLV object, set a tag, encode to bytes, decode back.

from uttlv import Tlv

tlv = Tlv()
tlv[0x01] = b'data'
encoded = tlv.to_bytes()
print('Encoded:', encoded.hex())

decoded = Tlv()
decoded.from_bytes(encoded)
assert decoded[0x01] == b'data'