Python: rtemis.a3

Python implementation of the Amino Acid Annotation (A3) format — a structured JSON format for amino acid sequences with site, region, PTM, processing, and variant annotations.

Part of the rtemis-org/a3 monorepo, which provides A3 implementations in Python, TypeScript, R, Julia, and Rust.

Installation

pip install rtemis-a3
# or with uv
uv add rtemis-a3

Quick Start

from rtemis.a3 import create_a3

a3 = create_a3(
    "MKTAYIAKQR",
    site={
        "Active site": {"index": [3, 5], "type": "activeSite"},
    },
    region={
        "Repeat 1": {"index": [[1, 4]], "type": ""},
    },
    ptm={
        "Phosphorylation": {"index": [7], "type": ""},
    },
    variant=[{"position": 3, "from": "K", "to": "R"}],
    metadata={
        "uniprot_id":  "P12345",
        "description": "Example protein",
        "organism":    "Homo sapiens",
    },
)

len(a3.sequence)   # 10

Parsing JSON

from rtemis.a3 import a3_from_json, A3ValidationError, A3ParseError

try:
    a3 = a3_from_json(json_string)
except A3ValidationError as e:
    print(e.errors)  # list of Pydantic error dicts with field paths
except A3ParseError as e:
    print(e)         # malformed JSON

File I/O

from rtemis.a3 import read_a3json, write_a3json

a3 = read_a3json("protein.json")
write_a3json(a3, "output.json", indent=2)

Serialization

from rtemis.a3 import a3_to_json

json_string = a3_to_json(a3)           # compact
json_string = a3_to_json(a3, indent=2) # pretty-printed

Wire Format

{
  "sequence": "MKTAYIAKQR",
  "annotations": {
    "site":       { "Active site": { "index": [3, 5],   "type": "activeSite" } },
    "region":     { "Repeat 1":    { "index": [[1, 4]], "type": "" } },
    "ptm":        { "Phospho":     { "index": [7],      "type": "" } },
    "processing": {},
    "variant":    [{ "position": 3, "from": "K", "to": "R" }]
  },
  "metadata": {
    "uniprot_id":  "P12345",
    "description": "Example protein",
    "reference":   "",
    "organism":    "Homo sapiens"
  }
}

All five annotation families are always present in output. Each annotation entry is { index, type } — bare arrays are rejected. Positions are 1-based, sorted, and deduplicated. Ranges are [start, end] pairs (start < end), sorted by start; overlapping ranges are rejected.

API

Construction

Function	Description
`create_a3(sequence, *, site, region, ptm, processing, variant, metadata)`	Build and validate an A3 object

Queries

Function	Description
`residue_at(a3, position)`	Residue at a 1-based position; raises `ValueError` if out of bounds
`variants_at(a3, position)`	All variant records at a 1-based position

Serialization / I/O

Function	Description
`a3_from_json(text)`	Parse a JSON string into an A3 object
`a3_to_json(a3, *, indent)`	Serialize an A3 object to a JSON string
`read_a3json(path)`	Read an A3 JSON file from disk
`write_a3json(a3, path, *, indent)`	Write an A3 object to a JSON file

Pydantic Model Hierarchy

A3
 ├── sequence:    str
 ├── annotations: A3Annotations
 │   ├── site:        dict[str, SiteEntry]    (position index)
 │   ├── region:      dict[str, RegionEntry]  (range index)
 │   ├── ptm:         dict[str, FlexEntry]    (position or range index)
 │   ├── processing:  dict[str, FlexEntry]    (position or range index)
 │   └── variant:     list[VariantRecord]
 └── metadata:    A3Metadata
     ├── uniprot_id, description, reference, organism

All models are immutable (frozen=True). Users never construct them directly — use create_a3 or a3_from_json instead.

License

MPL-2.0

Python: rtemis.a3

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