psimodpy 0.1.1

Python library for the PSI-MOD protein modification ontology

psimodpy

Python library for parsing and querying the PSI-MOD protein modification ontology.

• Zero dependencies
• Bundled PSI-MOD data (2,116 entries) — works offline out of the box
• Typed, immutable data models (py.typed / PEP 561)

Installation

pip install psimodpy

Or with uv:

uv add psimodpy

Requires Python 3.12+. No third-party dependencies.

Quick Start

import psimodpy

# Load the bundled PSI-MOD database
db = psimodpy.load()

# Lookup by ID
entry = db[46]  # O-phospho-L-serine
print(entry.name)       # "O-phospho-L-serine"
print(entry.diff_mono)  # 79.966331
print(entry.origin)     # AminoAcid.SER

# Lookup by name (case-insensitive)
entry = db.get_by_name("O-phospho-L-serine")

# Also accepts MOD:NNNNN format
entry = db.get_by_id("MOD:00046")

# Search across names, definitions, and synonyms
results = db.search("phospho")

# Find all modifications for an amino acid
ser_mods = db.get_by_origin("S")

# Filter entries
slim = db.filter(slim_only=True, include_obsolete=False)

# Formula parsing
print(entry.dict_diff_formula)      # {'C': 0, 'H': 0, 'N': 0, 'O': 3, 'P': 1}
print(entry.proforma_diff_formula)  # 'O3P'

API Overview

Loading

Function	Description
psimodpy.load()	Load the bundled PSI-MOD database.
psimodpy.load_from(path)	Load from a custom OBO file.
psimodpy.parse_obo(path)	Parse an OBO file into a database.
psimodpy.download_obo()	Download the latest OBO file from GitHub.

PsiModDatabase

Method	Description
db[id]	Lookup by ID (int or "MOD:00046"), raises KeyError.
db.get_by_id(id)	Lookup by ID, returns None if missing.
db.get_by_name(name)	Case-insensitive name lookup.
db.search(query)	Full-text search in names, definitions, synonyms.
db.get_by_origin(aa)	Find entries by amino acid origin.
db.get_parents(entry)	Direct parent entries (is_a hierarchy).
db.get_children(entry)	Direct child entries.
db.get_related(entry, type)	Follow relationship edges (derives_from, contains, etc.).
db.filter(...)	Filter by obsolete/slim status.

PsiModEntry

Each entry provides: id, name, definition, synonyms, is_a, relationships, origin, diff_mono, diff_avg, diff_formula, mass_mono, mass_avg, formula, term_spec, source, formal_charge, xref_unimod, xref_uniprot_ptm, xref_gnome, xref_remap, in_slim_subset, is_obsolete.

Computed properties: dict_diff_formula, dict_formula, proforma_diff_formula.

Data Types

• AminoAcid — single-letter amino acid codes
• Crosslink — multi-residue or MOD-referenced origins
• Synonym / SynonymType — typed synonyms
• Relationship / RelationshipType — directed relationships
• TermSpec — positional specificity
• Source — modification origin

Development

just install   # install dependencies with uv
just lint      # ruff check
just format    # ruff format
just ty        # ty type check
just test      # pytest
just check     # lint + type check + test

Related Projects

Package	Description
unimodpy	Parse and query the UNIMOD mass spectrometry modifications database
uniprotptmpy	Parse and query the UniProt PTM controlled vocabulary

License

MIT