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# fmt: off
"""Reads chemical data in SDF format (wraps the molfile format).
See https://en.wikipedia.org/wiki/Chemical_table_file#SDF
"""
from typing import TextIO
from ase.atoms import Atoms
from ase.utils import reader
def get_num_atoms_sdf_v2000(first_line: str) -> int:
"""Parse the first line extracting the number of atoms.
The V2000 dialect uses a fixed field length of 3, which means there
won't be space between the numbers if there are 100+ atoms, and
the format doesn't support 1000+ atoms at all.
http://biotech.fyicenter.com/1000024_SDF_File_Format_Specification.html
"""
return int(first_line[0:3]) # first three characters
@reader
def read_sdf(file_obj: TextIO) -> Atoms:
"""Read the sdf data and compose the corresponding Atoms object."""
lines = file_obj.readlines()
# first three lines header
del lines[:3]
num_atoms = get_num_atoms_sdf_v2000(lines.pop(0))
positions = []
symbols = []
for line in lines[:num_atoms]:
x, y, z, symbol = line.split()[:4]
symbols.append(symbol)
positions.append((float(x), float(y), float(z)))
return Atoms(symbols=symbols, positions=positions)
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