CIFFileHandler

molsysmt.native.CIFFileHandler is the native low-level file handler class in MolSysMT for reading and parsing Macromolecular Crystallographic Information File (.cif / .mmcif) formats.

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Overview and Handler Role

CIFFileHandler provides dictionary-based category parsing for mmCIF files. It processes loop blocks, category key-value pairs (_atom_site.*, _struct_conf.*), and large macromolecular structures where standard PDB column limits (99,999 atoms) are exceeded.

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Class Attributes and Parsed Records

Inside CIFFileHandler, mmCIF syntax categories are stored in parsed dictionaries:

Attribute / Property	Data Type	Description
file	File Handle / Stream	Active file handle pointing to mmCIF file or text buffer.
categories	Dictionary	Dictionary mapping mmCIF category headers (_atom_site, _cell, _entity) to value tables.
content	Dictionary	Standardized content dictionary prepared for conversion to molsysmt.Topology and molsysmt.Structures.

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Practical Usage and Streaming Workflow

import molsysmt as msm
from molsysmt.native import CIFFileHandler

# 1. Instantiate CIFFileHandler
handler = CIFFileHandler("complex.cif", io_mode="r")

# 2. Inspect mmCIF categories
categories = handler.categories

# 3. Close stream
handler.close()

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Performance and I/O Invariants

• Arbitrary Size Scaling: Handles large macromolecular assemblies without atom serial number truncation.

• Robust Category Lexer: Parses standard STAR/mmCIF token syntax and looped tables.