Source code for MDAnalysis.coordinates.PDB

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# R. J. Gowers, M. Linke, J. Barnoud, T. J. E. Reddy, M. N. Melo, S. L. Seyler,
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# MDAnalysis: A Python package for the rapid analysis of molecular dynamics
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# doi: 10.25080/majora-629e541a-00e
# N. Michaud-Agrawal, E. J. Denning, T. B. Woolf, and O. Beckstein.
# MDAnalysis: A Toolkit for the Analysis of Molecular Dynamics Simulations.
# J. Comput. Chem. 32 (2011), 2319--2327, doi:10.1002/jcc.21787

"""PDB structure files in MDAnalysis --- :mod:`MDAnalysis.coordinates.PDB`

MDAnalysis reads coordinates from PDB files and additional optional
data such as B-factors. It is also possible to substitute a PDB file
instead of PSF file in order to define the list of atoms (but no
connectivity information will be available in this case).

PDB files contain both coordinate and atom information. It is also possible to
write trajectories as multi-frame (or multi-model) PDB files. This is not very
space efficient but is sometimes the lowest common denominator for exchanging
trajectories. Single frame and multi-frame PDB files are automatically
recognized; the only difference is thath the single-frame PDB is represented as
a trajectory with only one frame.

In order to write a selection to a PDB file one typically uses the
:meth:`MDAnalysis.core.groups.AtomGroup.write` method of the selection::

  calphas = universe.select_atoms("name CA")

This uses the coordinates from the current timestep of the trajectory.

In order to write a PDB trajectory one needs to first obtain a multi-frame
writer (keyword *multiframe* = ``True``) and then iterate through the
trajectory, while writing each frame::

  calphas = universe.select_atoms("name CA")
  with MDAnalysis.Writer("calpha_traj.pdb", multiframe=True) as W:
      for ts in u.trajectory:

It is important to *always close the trajectory* when done because only at this
step is the final END_ record written, which is required by the `PDB 3.2
standard`_. Using the writer as a context manager ensures that this always


A pure-Python implementation for PDB files commonly encountered in MD
simulations comes under the names :class:`PDBReader` and :class:`PDBWriter`. It
only implements a subset of the `PDB 3.2 standard`_ and also allows some
typical enhancements such as 4-letter resids (introduced by CHARMM/NAMD).

The :class:`PDBReader` can read multi-frame PDB files and represents
them as a trajectory. The :class:`PDBWriter` can write single and
multi-frame PDB files as specified by the *multiframe* keyword. By default, it
writes single frames. On the other hand, the :class:`MultiPDBWriter` is set up
to write a PDB trajectory by default (equivalent to using *multiframe* =

Examples for working with PDB files

A **single frame PDB** can be written with the
:meth:`~MDAnalysis.core.groups.AtomGroup.write` method of any

   protein = u.select_atoms("protein")

Alternatively, get the single frame writer and supply the

  protein = u.select_atoms("protein")
  with MDAnalysis.Writer("protein.pdb") as pdb:

In order to write a **multi-frame PDB trajectory** from a universe *u* one can
do the following::

  with MDAnalysis.Writer("all.pdb", multiframe=True) as pdb:
      for ts in u.trajectory:

Similarly, writing only a protein::

  protein = u.select_atoms("protein")
  with MDAnalysis.Writer("protein.pdb", multiframe=True) as pdb:
      for ts in u.trajectory:


.. versionchanged:: 0.16.0
   PDB readers and writers based on :class:`Bio.PDB.PDBParser` were retired and

.. autoclass:: PDBReader

.. autoclass:: PDBWriter

   .. automethod:: _check_pdb_coordinates
   .. automethod:: _write_pdb_bonds
   .. automethod:: _update_frame
   .. automethod:: _write_timestep

.. autoclass:: MultiPDBWriter

.. autoclass:: ExtendedPDBReader

.. _`PDB 3.2 standard`:

from __future__ import absolute_import

from six.moves import range, zip
from six import raise_from, StringIO, BytesIO

import os
import errno
import itertools
import textwrap
import warnings
import logging
import collections
import numpy as np

from ..lib import util
from . import base
from ..topology.core import guess_atom_element
from ..exceptions import NoDataError

logger = logging.getLogger("MDAnalysis.coordinates.PBD")

# Pairs of residue name / atom name in use to deduce PDB formatted atom names
Pair = collections.namedtuple('Atom', 'resname name')

[docs]class PDBReader(base.ReaderBase): """PDBReader that reads a `PDB-formatted`_ file, no frills. The following *PDB records* are parsed (see `PDB coordinate section`_ for details): - *CRYST1* for unitcell A,B,C, alpha,beta,gamma - *ATOM* or *HETATM* for serial,name,resName,chainID,resSeq,x,y,z,occupancy,tempFactor - *HEADER* (:attr:`header`), *TITLE* (:attr:`title`), *COMPND* (:attr:`compound`), *REMARK* (:attr:`remarks`) - all other lines are ignored Reads multi-`MODEL`_ PDB files as trajectories. .. _PDB-formatted: .. _PDB coordinate section: .. _MODEL: ============= ============ =========== ============================================= COLUMNS DATA TYPE FIELD DEFINITION ============= ============ =========== ============================================= 1 - 6 Record name "CRYST1" 7 - 15 Real(9.3) a a (Angstroms). 16 - 24 Real(9.3) b b (Angstroms). 25 - 33 Real(9.3) c c (Angstroms). 34 - 40 Real(7.2) alpha alpha (degrees). 41 - 47 Real(7.2) beta beta (degrees). 48 - 54 Real(7.2) gamma gamma (degrees). 1 - 6 Record name "ATOM " 7 - 11 Integer serial Atom serial number. 13 - 16 Atom name Atom name. 17 Character altLoc Alternate location indicator. 18 - 21 Residue name resName Residue name. 22 Character chainID Chain identifier. 23 - 26 Integer resSeq Residue sequence number. 27 AChar iCode Code for insertion of residues. 31 - 38 Real(8.3) x Orthogonal coordinates for X in Angstroms. 39 - 46 Real(8.3) y Orthogonal coordinates for Y in Angstroms. 47 - 54 Real(8.3) z Orthogonal coordinates for Z in Angstroms. 55 - 60 Real(6.2) occupancy Occupancy. 61 - 66 Real(6.2) tempFactor Temperature factor. 67 - 76 String segID (unofficial CHARMM extension ?) 77 - 78 LString(2) element Element symbol, right-justified. 79 - 80 LString(2) charge Charge on the atom. ============= ============ =========== ============================================= Notes ----- If a system does not have unit cell parameters (such as in electron microscopy structures), the PDB file format requires the CRYST1_ field to be provided with unitary values (cubic box with sides of 1 Å) and an appropriate REMARK. If unitary values are found within the CRYST1_ field, :code:`PDBReader` will not set unit cell dimensions (which will take the default value :code:`np.zeros(6)`, see Issue #2698) and it will warn the user. .. _CRYST1: See Also -------- :class:`PDBWriter` :class:`PDBReader` .. versionchanged:: 0.11.0 * Frames now 0-based instead of 1-based * New :attr:`title` (list with all TITLE lines). .. versionchanged:: 0.19.1 Can now read PDB files with DOS line endings .. versionchanged:: 0.20.0 Strip trajectory header of trailing spaces and newlines .. versionchanged:: 1.0.0 Raise user warning for CRYST1_ record with unitary valuse (cubic box with sides of 1 Å) and do not set cell dimensions. """ format = ['PDB', 'ENT'] units = {'time': None, 'length': 'Angstrom'} def __init__(self, filename, **kwargs): """Read coordinates from *filename*. *filename* can be a gzipped or bzip2ed compressed PDB file. If the pdb file contains multiple MODEL records then it is read as a trajectory where the MODEL numbers correspond to frame numbers. """ super(PDBReader, self).__init__(filename, **kwargs) try: self.n_atoms = kwargs['n_atoms'] except KeyError: # hackish, but should work and keeps things DRY # regular MDA usage via Universe doesn't follow this route from MDAnalysis.topology import PDBParser with PDBParser.PDBParser(self.filename) as p: top = p.parse() self.n_atoms = top.n_atoms self.model_offset = kwargs.pop("model_offset", 0) # dummy/default variables as these are read header = "" title = [] compound = [] remarks = [] self.ts = self._Timestep(self.n_atoms, **self._ts_kwargs) # Record positions in file of CRYST and MODEL headers # then build frame offsets to start at the minimum of these # This allows CRYST to come either before or after MODEL # This assumes that **either** # - pdbfile has a single CRYST (NVT) # - pdbfile has a CRYST for every MODEL (NPT) models = [] crysts = [] # hack for streamIO if isinstance(filename, util.NamedStream) and isinstance(, StringIO): = BytesIO( pdbfile = self._pdbfile = util.anyopen(filename, 'rb') line = "magical" while line: # need to use readline so tell gives end of line # (rather than end of current chunk) line = pdbfile.readline() if line[:5] == b'MODEL': models.append(pdbfile.tell()) elif line[:5] == b'CRYST': # remove size of line to get **start** of CRYST line crysts.append(pdbfile.tell() - len(line)) elif line[:6] == b'HEADER': # classification = line[10:50] # date = line[50:59] # idCode = line[62:66] header = line[10:66].strip().decode() elif line[:5] == b'TITLE': title.append(line[8:80].strip().decode()) elif line[:6] == b'COMPND': compound.append(line[7:80].strip().decode()) elif line[:6] == b'REMARK': remarks.append(line[6:].strip().decode()) end = pdbfile.tell() # where the file ends self.header = header self.title = title self.compound = compound self.remarks = remarks if not models: # No model entries # so read from start of file to read first frame models.append(0) if len(crysts) == len(models): offsets = [min(a, b) for a, b in zip(models, crysts)] else: offsets = models # Position of the start of each frame self._start_offsets = offsets # Position of the end of each frame self._stop_offsets = offsets[1:] + [end] self.n_frames = len(offsets) self._read_frame(0)
[docs] def Writer(self, filename, **kwargs): """Returns a PDBWriter for *filename*. Parameters ---------- filename : str filename of the output PDB file Returns ------- :class:`PDBWriter` """ kwargs.setdefault('multiframe', self.n_frames > 1) return PDBWriter(filename, **kwargs)
def _reopen(self): # Pretend the current TS is -1 (in 0 based) so "next" is the # 0th frame self.close() self._pdbfile = util.anyopen(self.filename, 'rb') self.ts.frame = -1 def _read_next_timestep(self, ts=None): if ts is None: ts = self.ts else: # TODO: cleanup _read_frame() to use a "free" Timestep raise NotImplementedError("PDBReader cannot assign to a timestep") # frame is 1-based. Normally would add 1 to frame before calling # self._read_frame to retrieve the subsequent ts. But self._read_frame # assumes it is being passed a 0-based frame, and adjusts. frame = self.frame + 1 return self._read_frame(frame) def _read_frame(self, frame): """ Read frame from PDB file. Notes ----- When the CRYST1_ record has unitary values (cubic box with sides of 1 Å), cell dimensions are considered fictitious. An user warning is raised and cell dimensions are set to :code:`np.zeros(6)` (see Issue #2698) .. versionchanged:: 1.0.0 Raise user warning for CRYST1_ record with unitary valuse (cubic box with sides of 1 Å) and do not set cell dimensions. """ try: start = self._start_offsets[frame] stop = self._stop_offsets[frame] except IndexError: # out of range of known frames raise_from(IOError, None) pos = 0 occupancy = np.ones(self.n_atoms) # Seek to start and read until start of next frame chunk = - start).decode() tmp_buf = [] for line in chunk.splitlines(): if line[:6] in ('ATOM ', 'HETATM'): # we only care about coordinates tmp_buf.append([line[30:38], line[38:46], line[46:54]]) # TODO import bfactors - might these change? try: # does an implicit str -> float conversion occupancy[pos] = line[54:60] except ValueError: # Be tolerant for ill-formated or empty occupancies pass pos += 1 elif line[:6] == 'CRYST1': # does an implicit str -> float conversion try: cell_dims = np.array([line[6:15], line[15:24], line[24:33], line[33:40], line[40:47], line[47:54]], dtype=np.float32) except ValueError: warnings.warn("Failed to read CRYST1 record, " "possibly invalid PDB file, got:\n{}" "".format(line)) else: if np.allclose(cell_dims, np.array([1.0, 1.0, 1.0, 90.0, 90.0, 90.0])): # FIXME: Dimensions set to zeros. # FIXME: This might change with Issue #2698 warnings.warn("1 A^3 CRYST1 record," " this is usually a placeholder." " Unit cell dimensions will be set" " to zeros.") else: self.ts._unitcell[:] = cell_dims # check if atom number changed if pos != self.n_atoms: raise ValueError("Inconsistency in file '{}': The number of atoms " "({}) in trajectory frame {} differs from the " "number of atoms ({}) in the corresponding " "topology.\nTrajectories with varying numbers of " "atoms are currently not supported." "".format(self.filename, pos, frame, self.n_atoms)) # doing the conversion from list to array at the end is faster self.ts.positions = tmp_buf if self.convert_units: # both happen inplace self.convert_pos_from_native(self.ts._pos) self.convert_pos_from_native(self.ts._unitcell[:3]) self.ts.frame = frame['occupancy'] = occupancy return self.ts
[docs] def close(self): self._pdbfile.close()
[docs]class PDBWriter(base.WriterBase): """PDB writer that implements a subset of the `PDB 3.2 standard`_ . PDB format as used by NAMD/CHARMM: 4-letter resnames and segID are allowed, altLoc is written. The :class:`PDBWriter` can be used to either dump a coordinate set to a PDB file (operating as a "single frame writer", selected with the constructor keyword *multiframe* = ``False``, the default) or by writing a PDB "movie" (multi frame mode, *multiframe* = ``True``), consisting of multiple models (using the MODEL_ and ENDMDL_ records). .. _`PDB 3.2 standard`: .. _MODEL: .. _ENDMDL: .. _CONECT: Note ---- Writing bonds currently only works when writing a whole :class:`Universe` and if bond information is available in the topology. (For selections smaller than the whole :class:`Universe`, the atom numbering in the CONECT_ records would not match the numbering of the atoms in the new PDB file and therefore a :exc:`NotImplementedError` is raised.) The maximum frame number that can be stored in a PDB file is 9999 and it will wrap around (see :meth:`MODEL` for further details). The CRYST1_ record specifies the unit cell. This record is set to unitary values (cubic box with sides of 1 Å) if unit cell dimensions are not set (:code:`None` or :code:`np.zeros(6)`, see Issue #2698). See Also -------- This class is identical to :class:`MultiPDBWriter` with the one exception that it defaults to writing single-frame PDB files as if `multiframe` = ``False`` was selected. .. versionchanged:: 0.7.5 Initial support for multi-frame PDB files. .. versionchanged:: 0.7.6 The *multiframe* keyword was added to select the writing mode. The writing of bond information (CONECT_ records) is now disabled by default but can be enabled with the *bonds* keyword. .. versionchanged:: 0.11.0 Frames now 0-based instead of 1-based .. versionchanged:: 0.14.0 PDB doesn't save charge information .. versionchanged:: 0.20.0 Strip trajectory header of trailing spaces and newlines .. versionchanged:: 1.0.0 ChainID now comes from the last character of segid, as stated in the documentation. An indexing issue meant it previously used the first charater (Issue #2224) """ fmt = { 'ATOM': ( "ATOM {serial:5d} {name:<4s}{altLoc:<1s}{resName:<4s}" "{chainID:1s}{resSeq:4d}{iCode:1s}" " {pos[0]:8.3f}{pos[1]:8.3f}{pos[2]:8.3f}{occupancy:6.2f}" "{tempFactor:6.2f} {segID:<4s}{element:>2s}\n"), 'REMARK': "REMARK {0}\n", 'COMPND': "COMPND {0}\n", 'HEADER': "HEADER {0}\n", 'TITLE': "TITLE {0}\n", 'MODEL': "MODEL {0:>4d}\n", 'NUMMDL': "NUMMDL {0:5d}\n", 'ENDMDL': "ENDMDL\n", 'END': "END\n", 'CRYST1': ("CRYST1{box[0]:9.3f}{box[1]:9.3f}{box[2]:9.3f}" "{ang[0]:7.2f}{ang[1]:7.2f}{ang[2]:7.2f} " "{spacegroup:<11s}{zvalue:4d}\n"), 'CONECT': "CONECT{0}\n" } format = ['PDB', 'ENT'] units = {'time': None, 'length': 'Angstrom'} pdb_coor_limits = {"min": -999.9995, "max": 9999.9995} #: wrap comments into REMARK records that are not longer than # :attr:`remark_max_length` characters. remark_max_length = 66 multiframe = False # These attributes are used to deduce how to format the atom name. ions = ('FE', 'AS', 'ZN', 'MG', 'MN', 'CO', 'BR', 'CU', 'TA', 'MO', 'AL', 'BE', 'SE', 'PT', 'EU', 'NI', 'IR', 'RH', 'AU', 'GD', 'RU') # Mercurial can be confused for hydrogen gamma. Yet, mercurial is # rather rare in the PDB. Here are all the residues that contain # mercurial. special_hg = ('CMH', 'EMC', 'MBO', 'MMC', 'HGB', 'BE7', 'PMB') # Chloride can be confused for a carbon. Here are the residues that # contain chloride. special_cl = ('0QE', 'CPT', 'DCE', 'EAA', 'IMN', 'OCZ', 'OMY', 'OMZ', 'UN9', '1N1', '2T8', '393', '3MY', 'BMU', 'CLM', 'CP6', 'DB8', 'DIF', 'EFZ', 'LUR', 'RDC', 'UCL', 'XMM', 'HLT', 'IRE', 'LCP', 'PCI', 'VGH') # In these pairs, the atom name is aligned on the first column # (column 13). include_pairs = (Pair('OEC', 'CA1'), Pair('PLL', 'PD'), Pair('OEX', 'CA1')) # In these pairs, the atom name is aligned on the second column # (column 14), but other rules would align them on the first column. exclude_pairs = (Pair('C14', 'C14'), Pair('C15', 'C15'), Pair('F9F', 'F9F'), Pair('OAN', 'OAN'), Pair('BLM', 'NI'), Pair('BZG', 'CO'), Pair('BZG', 'NI'), Pair('VNL', 'CO1'), Pair('VNL', 'CO2'), Pair('PF5', 'FE1'), Pair('PF5', 'FE2'), Pair('UNL', 'UNL')) def __init__(self, filename, bonds="conect", n_atoms=None, start=0, step=1, remarks="Created by PDBWriter", convert_units=True, multiframe=None): """Create a new PDBWriter Parameters ---------- filename: str name of output file start: int (optional) starting timestep (the first frame will have MODEL number `start` + 1 because the PDB standard prescribes MODEL numbers starting at 1) step: int (optional) skip between subsequent timesteps remarks: str (optional) comments to annotate pdb file (added to the *TITLE* record); note that any remarks from the trajectory that serves as input are written to REMARK records with lines longer than :attr:`remark_max_length` (66 characters) being wrapped. convert_units: bool (optional) units are converted to the MDAnalysis base format; [``True``] bonds : {"conect", "all", None} (optional) If set to "conect", then only write those bonds that were already defined in an input PDB file as PDB CONECT_ record. If set to "all", write all bonds (including guessed ones) to the file. ``None`` does not write any bonds. The default is "conect". multiframe: bool (optional) ``False``: write a single frame to the file; ``True``: create a multi frame PDB file in which frames are written as MODEL_ ... ENDMDL_ records. If ``None``, then the class default is chosen. [``None``] .. _CONECT: .. _MODEL: .. _ENDMDL: """ # n_atoms = None : dummy keyword argument # (not used, but Writer() always provides n_atoms as the second argument) # TODO: - remarks should be a list of lines and written to REMARK # - additional title keyword could contain line for TITLE self.filename = filename # convert length and time to base units self.convert_units = convert_units self._multiframe = self.multiframe if multiframe is None else multiframe self.bonds = bonds if start < 0: raise ValueError("'Start' must be a positive value") self.start = self.frames_written = start self.step = step self.remarks = remarks self.pdbfile = util.anyopen(self.filename, 'wt') # open file on init self.has_END = False self.first_frame_done = False
[docs] def close(self): """Close PDB file and write END record""" if hasattr(self, 'pdbfile') and self.pdbfile is not None: if not self.has_END: self.END() else: logger.warning("END record has already been written" " before the final closing of the file") self.pdbfile.close() self.pdbfile = None
def _write_pdb_title(self): if self._multiframe: self.TITLE("MDANALYSIS FRAMES FROM {0:d}, STEP {1:d}: {2!s}" "".format(self.start, self.step, self.remarks)) else: self.TITLE("MDANALYSIS FRAME {0:d}: {1!s}" "".format(self.start, self.remarks)) def _write_pdb_header(self): """ Write PDB header. The HEADER_ record is set to :code: `trajectory.header`. The TITLE_ record explicitly mentions MDAnalysis and contains information about trajectory frame(s). The COMPND_ record is set to :code:`trajectory.compound`. The REMARKS_ records are set to :code:`u.trajectory.remarks` The CRYST1_ record specifies the unit cell. This record is set to unitary values (cubic box with sides of 1 Å) if unit cell dimensions are not set. .. _COMPND: .. _REMARKS: .. versionchanged: 1.0.0 Fix writing of PDB file without unit cell dimensions (Issue #2679). If cell dimensions are not found, unitary values (cubic box with sides of 1 Å) are used (PDB standard for CRYST1_). """ if self.first_frame_done is True: return self.first_frame_done = True u = self.obj.universe self.HEADER(u.trajectory) self._write_pdb_title() self.COMPND(u.trajectory) try: # currently inconsistent: DCDReader gives a string, # PDB*Reader a list, so always get a list # split long single lines into chunks of 66 chars remarks = [] for line in util.asiterable(u.trajectory.remarks): remarks.extend(textwrap.wrap(line, self.remark_max_length)) self.REMARK(*remarks) except AttributeError: pass # FIXME: Values for meaningless cell dimensions are not consistent. # FIXME: See Issue #2698. Here we check for both None and zeros if u.dimensions is None or np.allclose(u.dimensions, np.zeros(6)): # Unitary unit cell by default. See PDB standard: # self.CRYST1(np.array([1.0, 1.0, 1.0, 90.0, 90.0, 90.0])) # Add CRYST1 REMARK (285) # The SCALE record is not included # (We are only implementing a subset of the PDB standard) self.REMARK("285 UNITARY VALUES FOR THE UNIT CELL AUTOMATICALLY SET") self.REMARK("285 BY MDANALYSIS PDBWRITER BECAUSE UNIT CELL INFORMATION") self.REMARK("285 WAS MISSING.") self.REMARK("285 PROTEIN DATA BANK CONVENTIONS REQUIRE THAT") self.REMARK("285 CRYST1 RECORD IS INCLUDED, BUT THE VALUES ON") self.REMARK("285 THIS RECORD ARE MEANINGLESS.") warnings.warn("Unit cell dimensions not found. " "CRYST1 record set to unitary values.") else: self.CRYST1(self.convert_dimensions_to_unitcell(u.trajectory.ts))
[docs] def _check_pdb_coordinates(self): """Check if the coordinate values fall within the range allowed for PDB files. Deletes the output file if this is the first frame or if frames have already been written (in multi-frame mode) adds a REMARK instead of the coordinates and closes the file. Raises ------ ValueError if the coordinates fail the check. .. versionchanged: 1.0.0 Check if :attr:`filename` is `StringIO` when attempting to remove a PDB file with invalid coordinates (Issue #2512) """ atoms = self.obj.atoms # make sure to use atoms (Issue 46) # can write from selection == Universe (Issue 49) coor = atoms.positions # check if any coordinates are illegal (coordinates are already in # Angstroem per package default) if self.has_valid_coordinates(self.pdb_coor_limits, coor): return True # note the precarious close() here: we know that the file is open and # we now prepare to remove what we have already written (header and # such) or add a REMARK (which allows the user to look at the # previously written frames) if self.frames_written > 1: self.REMARK("Incomplete multi-frame trajectory.", "Coordinates for the current frame cannot be " "represented in the PDB format.") self.close() else: self.close() try: os.remove(self.filename) except OSError as err: if err.errno == errno.ENOENT: pass else: raise except TypeError: if isinstance(self.filename, StringIO): pass else: raise raise ValueError("PDB files must have coordinate values between " "{0:.3f} and {1:.3f} Angstroem: file writing was " "aborted.".format(self.pdb_coor_limits["min"], self.pdb_coor_limits["max"]))
[docs] def _write_pdb_bonds(self): """Writes out all the bond records""" if self.bonds is None: return if not self.obj or not hasattr(self.obj.universe, 'bonds'): return mapping = {index: i for i, index in enumerate(self.obj.atoms.indices)} bondset = set(itertools.chain(*(a.bonds for a in self.obj.atoms))) if self.bonds == "conect": # Write out only the bonds that were defined in CONECT records bonds = ((bond[0].index, bond[1].index) for bond in bondset if not bond.is_guessed) elif self.bonds == "all": bonds = ((bond[0].index, bond[1].index) for bond in bondset) else: raise ValueError("bonds has to be either None, 'conect' or 'all'") con = collections.defaultdict(list) for a1, a2 in bonds: if not (a1 in mapping and a2 in mapping): continue con[a2].append(a1) con[a1].append(a2) atoms = np.sort(self.obj.atoms.indices) conect = ([mapping[a]] + sorted([mapping[at] for at in con[a]]) for a in atoms if a in con) for c in conect: self.CONECT(c)
[docs] def _update_frame(self, obj): """Method to initialize important attributes in writer from a AtomGroup or Universe *obj*. Attributes initialized/updated: * :attr:`PDBWriter.obj` (the entity that provides topology information *and* coordinates, either a :class:`~MDAnalysis.core.groups.AtomGroup` or a whole :class:`~MDAnalysis.core.universe.Universe`) * :attr:`PDBWriter.trajectory` (the underlying trajectory :class:`~MDAnalysis.coordinates.base.Reader`) * :attr:`PDBWriter.timestep` (the underlying trajectory :class:`~MDAnalysis.coordinates.base.Timestep`) Before calling :meth:`_write_next_frame` this method **must** be called at least once to enable extracting topology information from the current frame. """ if isinstance(obj, base.Timestep): raise TypeError("PDBWriter cannot write Timestep objects " "directly, since they lack topology information (" "atom names and types) required in PDB files") if len(obj.atoms) == 0: raise IndexError("Cannot write empty AtomGroup") # remember obj for some of other methods --- NOTE: this is an evil/lazy # hack... self.obj = obj self.ts = obj.universe.trajectory.ts
[docs] def write(self, obj): """Write object *obj* at current trajectory frame to file. *obj* can be a selection (i.e. a :class:`~MDAnalysis.core.groups.AtomGroup`) or a whole :class:`~MDAnalysis.core.universe.Universe`. The last letter of the :attr:`~MDAnalysis.core.groups.Atom.segid` is used as the PDB chainID (but see :meth:`~PDBWriter.ATOM` for details). Parameters ---------- obj The :class:`~MDAnalysis.core.groups.AtomGroup` or :class:`~MDAnalysis.core.universe.Universe` to write. """ self._update_frame(obj) self._write_pdb_header() # Issue 105: with write() ONLY write a single frame; use # write_all_timesteps() to dump everything in one go, or do the # traditional loop over frames self._write_next_frame(self.ts, multiframe=self._multiframe) self._write_pdb_bonds()
# END record is written when file is being close()d
[docs] def write_all_timesteps(self, obj): """Write all timesteps associated with *obj* to the PDB file. *obj* can be a :class:`~MDAnalysis.core.groups.AtomGroup` or a :class:`~MDAnalysis.core.universe.Universe`. The method writes the frames from the one specified as *start* until the end, using a step of *step* (*start* and *step* are set in the constructor). Thus, if *u* is a Universe then :: u.trajectory[-2] pdb = PDBWriter("out.pdb", u.atoms.n_atoms) pdb.write_all_timesteps(u) will write a PDB trajectory containing the last 2 frames and :: pdb = PDBWriter("out.pdb", u.atoms.n_atoms, start=12, step=2) pdb.write_all_timesteps(u) will be writing frames 12, 14, 16, ... .. versionchanged:: 0.11.0 Frames now 0-based instead of 1-based """ self._update_frame(obj) self._write_pdb_header() start, step = self.start, self.step traj = obj.universe.trajectory # Start from trajectory[0]/frame 0, if there are more than 1 frame. # If there is only 1 frame, the traj.frames is not like a python list: # accessing trajectory[-1] raises key error. if not start and traj.n_frames > 1: start = traj.frame for framenumber in range(start, len(traj), step): traj[framenumber] self._write_next_frame(self.ts, multiframe=True) self._write_pdb_bonds() self.close() # Set the trajectory to the starting position traj[start]
def _write_next_frame(self, ts=None, **kwargs): '''write a new timestep to the PDB file :Keywords: *ts* :class:`base.Timestep` object containing coordinates to be written to trajectory file; if ``None`` then :attr:`PDBWriter.ts`` is tried. *multiframe* ``False``: write a single frame (default); ``True`` behave as a trajectory writer .. Note:: Before using this method with another :class:`base.Timestep` in the *ts* argument, :meth:`PDBWriter._update_frame` *must* be called with the :class:`~MDAnalysis.core.groups.AtomGroup.Universe` as its argument so that topology information can be gathered. .. versionchanged:: 1.0.0 Renamed from `write_next_timestep` to `_write_next_frame`. ''' if ts is None: try: ts = self.ts except AttributeError: raise_from( NoDataError( "PBDWriter: no coordinate data to write to " "trajectory file" ), None) self._check_pdb_coordinates() self._write_timestep(ts, **kwargs) def _deduce_PDB_atom_name(self, atomname, resname): """Deduce how the atom name should be aligned. Atom name format can be deduced from the atom type, yet atom type is not always available. This function uses the atom name and residue name to deduce how the atom name should be formatted. The rules in use got inferred from an analysis of the PDB. See gist at <> for more details. """ if atomname == '': return '' if len(atomname) >= 4: return atomname[:4] elif len(atomname) == 1: return ' {} '.format(atomname) elif ((resname == atomname or atomname[:2] in self.ions or atomname == 'UNK' or (resname in self.special_hg and atomname[:2] == 'HG') or (resname in self.special_cl and atomname[:2] == 'CL') or Pair(resname, atomname) in self.include_pairs) and Pair(resname, atomname) not in self.exclude_pairs): return '{:<4}'.format(atomname) return ' {:<3}'.format(atomname)
[docs] def _write_timestep(self, ts, multiframe=False): """Write a new timestep *ts* to file Does unit conversion if necessary. By setting *multiframe* = ``True``, MODEL_ ... ENDMDL_ records are written to represent trajectory frames in a multi-model PDB file. (At the moment we do *not* write the NUMMDL_ record.) The *multiframe* = ``False`` keyword signals that the :class:`PDBWriter` is in single frame mode and no MODEL_ records are written. .. _MODEL: .. _ENDMDL: .. _NUMMDL: .. versionchanged:: 0.7.6 The *multiframe* keyword was added, which completely determines if MODEL records are written. (Previously, this was decided based on the underlying trajectory and only if ``len(traj) > 1`` would MODEL records have been written.) .. versionchanged:: 1.0.0 ChainID now comes from the last character of segid, as stated in the documentation. An indexing issue meant it previously used the first charater (Issue #2224) """ atoms = self.obj.atoms pos = atoms.positions if self.convert_units: pos = self.convert_pos_to_native(pos, inplace=False) if multiframe: self.MODEL(self.frames_written + 1) # Make zero assumptions on what information the AtomGroup has! # theoretically we could get passed only indices! def get_attr(attrname, default): """Try and pull info off atoms, else fake it attrname - the field to pull of AtomGroup (plural!) default - default value in case attrname not found """ try: return getattr(atoms, attrname) except AttributeError: if self.frames_written == 0: warnings.warn("Found no information for attr: '{}'" " Using default value of '{}'" "".format(attrname, default)) return np.array([default] * len(atoms)) altlocs = get_attr('altLocs', ' ') resnames = get_attr('resnames', 'UNK') icodes = get_attr('icodes', ' ') segids = get_attr('segids', ' ') resids = get_attr('resids', 1) occupancies = get_attr('occupancies', 1.0) tempfactors = get_attr('tempfactors', 0.0) atomnames = get_attr('names', 'X') for i, atom in enumerate(atoms): vals = {} vals['serial'] = util.ltruncate_int(i + 1, 5) # check for overflow here? vals['name'] = self._deduce_PDB_atom_name(atomnames[i], resnames[i]) vals['altLoc'] = altlocs[i][:1] vals['resName'] = resnames[i][:4] vals['chainID'] = segids[i][-1:] vals['resSeq'] = util.ltruncate_int(resids[i], 4) vals['iCode'] = icodes[i][:1] vals['pos'] = pos[i] # don't take off atom so conversion works vals['occupancy'] = occupancies[i] vals['tempFactor'] = tempfactors[i] vals['segID'] = segids[i][:4] vals['element'] = guess_atom_element(atomnames[i].strip())[:2] # .. _ATOM: self.pdbfile.write(self.fmt['ATOM'].format(**vals)) if multiframe: self.ENDMDL() self.frames_written += 1
[docs] def HEADER(self, trajectory): """Write HEADER_ record. .. _HEADER: .. versionchanged:: 0.20.0 Strip `trajectory.header` since it can be modified by the user and should be sanitized (Issue #2324) """ if not hasattr(trajectory, 'header'): return header = trajectory.header.strip() self.pdbfile.write(self.fmt['HEADER'].format(header))
[docs] def TITLE(self, *title): """Write TITLE_ record. .. _TITLE: """ line = " ".join(title) # TODO: should do continuation automatically self.pdbfile.write(self.fmt['TITLE'].format(line))
[docs] def REMARK(self, *remarks): """Write generic REMARK_ record (without number). Each string provided in *remarks* is written as a separate REMARK_ record. See also `REMARK (update)`_. .. _REMARK: .. _REMARK (update): """ for remark in remarks: self.pdbfile.write(self.fmt['REMARK'].format(remark))
def COMPND(self, trajectory): if not hasattr(trajectory, 'compound'): return compound = trajectory.compound for c in compound: self.pdbfile.write(self.fmt['COMPND'].format(c))
[docs] def CRYST1(self, dimensions, spacegroup='P 1', zvalue=1): """Write CRYST1_ record. """ self.pdbfile.write(self.fmt['CRYST1'].format( box=dimensions[:3], ang=dimensions[3:], spacegroup=spacegroup, zvalue=zvalue))
[docs] def MODEL(self, modelnumber): """Write the MODEL_ record. .. note:: The maximum MODEL number is limited to 9999 in the PDB standard (i.e., 4 digits). If frame numbers are larger than 9999, they will wrap around, i.e., 9998, 9999, 0, 1, 2, ... .. _MODEL: .. versionchanged:: 0.19.0 Maximum model number is enforced. """ self.pdbfile.write(self.fmt['MODEL'].format(int(str(modelnumber)[-4:])))
[docs] def END(self): """Write END_ record. Only a single END record is written. Calling END multiple times has no effect. Because :meth:`~PDBWriter.close` also calls this method right before closing the file it is recommended to *not* call :meth:`~PDBWriter.END` explicitly. .. _END: """ if not self.has_END: # only write a single END record self.pdbfile.write(self.fmt['END']) self.has_END = True
[docs] def ENDMDL(self): """Write the ENDMDL_ record. .. _ENDMDL: """ self.pdbfile.write(self.fmt['ENDMDL'])
[docs] def CONECT(self, conect): """Write CONECT_ record. .. _CONECT: """ conect = ["{0:5d}".format(entry + 1) for entry in conect] conect = "".join(conect) self.pdbfile.write(self.fmt['CONECT'].format(conect))
[docs]class ExtendedPDBReader(PDBReader): """PDBReader that reads a PDB-formatted file with five-digit residue numbers. This reader does not conform to the `PDB 3.2 standard`_ because it allows five-digit residue numbers that may take up columns 23 to 27 (inclusive) instead of being confined to 23-26 (with column 27 being reserved for the insertion code in the PDB standard). PDB files in this format are written by popular programs such as VMD_. See Also -------- :class:`PDBReader` .. _VMD: .. versionadded:: 0.8 """ format = "XPDB"
[docs]class MultiPDBWriter(PDBWriter): """PDB writer that implements a subset of the `PDB 3.2 standard`_ . PDB format as used by NAMD/CHARMM: 4-letter resnames and segID, altLoc is written. By default, :class:`MultiPDBWriter` writes a PDB "movie" (multi frame mode, *multiframe* = ``True``), consisting of multiple models (using the MODEL_ and ENDMDL_ records). .. _MODEL: .. _ENDMDL: .. _CONECT: See Also -------- This class is identical to :class:`PDBWriter` with the one exception that it defaults to writing multi-frame PDB files instead of single frames. .. versionadded:: 0.7.6 """ format = ['PDB', 'ENT'] multiframe = True # For Writer registration singleframe = False