Source code for MDAnalysis.selections.base

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Base classes for the selection writers

Specialized SelectionWriters are derived from
:class:`SelectionWriterBase`. Override the :meth:`~SelectionWriterBase._write_head`,
:meth:`~SelectionWriterBase._translate`, and :meth:`~SelectionWriterBase._write_tail`

.. autoclass:: SelectionWriterBase
   :members: __init__, write, _translate, _write_head, _write_tail, comment

.. autofunction:: join

import os.path

from ..lib import util
from . import _SELECTION_WRITERS

[docs]def join(seq, string="", func=None): """Create a list from sequence. *string* is appended to each element but the last. *func* is applied to every element before appending *string*. """ if func is None: func = lambda x: x return [func(x) + string for x in seq[:-1]] + [func(seq[-1])]
class _Selectionmeta(type): # Auto register upon class creation def __init__(cls, name, bases, classdict): type.__init__(type, name, bases, classdict) try: fmt = util.asiterable(classdict['format']) except KeyError: pass else: for f in fmt: if f is None: continue f = f.upper() _SELECTION_WRITERS[f] = cls
[docs]class SelectionWriterBase(metaclass=_Selectionmeta): """Export a selection in MDAnalysis to a format usable in an external package. The :class:`SelectionWriterBase` writes a selection string to a file that can be used in another package such as `VMD`_, `PyMOL`_, `Gromacs`_ or `CHARMM`_. In this way, analysis and visualization can be done with the best or most convenient tools at hand. :class:`SelectionWriterBase` is a base class and child classes are derived with the appropriate customizations for the package file format. .. _VMD: .. _PyMol: .. _CHARMM: .. _Gromacs: .. versionchanged:: 0.11.0 Can now also write to a :class:`~MDAnalysis.lib.util.NamedStream` instead of a normal file (using :class:`~MDAnalysis.lib.util.openany`). .. versionchanged:: 0.16.0 Remove the `wa` mode. The file is now open when the instance is created and closed with the :meth:`close` method or when exiting the `with` statement. """ #: Name of the format. format = None #: Extension of output files. ext = None #: Special character to continue a line across a newline. continuation = '' #: Comment format string; should contain '%s' or ``None`` for no comments. commentfmt = None default_numterms = 8
[docs] def __init__(self, filename, mode="w", numterms=None, preamble=None, **kwargs): """Set up for writing to *filename*. Parameters ---------- filename: output file mode: create a new file ("w"), or append ("a") to existing file ["w"] numterms: number of individual index numbers per line for output formats that write multiple entries in one line. If set to 0 or ``False`` then no special formatting is done [8] preamble: string that is written as a comment at the top of the file [] kwargs: use as defaults for :meth:`write` """ self.filename = util.filename(filename, ext=self.ext) if not mode in ('a', 'w'): raise ValueError("mode must be one of 'w', 'a', not {0!r}".format(mode)) self.mode = mode self._current_mode = mode[0] if numterms is None or numterms < 0: self.numterms = self.default_numterms elif numterms is False: self.numterms = 0 else: self.numterms = numterms self.preamble = preamble self.otherargs = kwargs # hack self.number = 0 self._outfile = util.anyopen(self.filename, mode=self._current_mode) self.write_preamble()
[docs] def comment(self, s): """Return string *s* interpolated into the comment format string. If no :attr:`SelectionWriterBase.commentfmt` is defined (None) then the empty string is returned because presumably there is no way to enter comments into the file. A newline is appended to non-empty strings. """ if self.commentfmt is None: return '' return self.commentfmt % s + '\n'
def write_preamble(self): """Write a header, depending on the file format.""" if self.preamble is None: return self._outfile.write(self.comment(self.preamble))
[docs] def write(self, selection, number=None, name=None, frame=None, mode=None): """Write selection to the output file. Parameters ---------- selection: a :class:`MDAnalysis.core.groups.AtomGroup` number: selection will be named "mdanalysis<number>" (``None`` auto increments between writes; useful when appending) [``None``] name: selection will be named *name* (instead of numbered) [``None``] frame: write selection of this frame (or the current one if ``None`` [``None``] """ u = selection.universe if frame is not None: u.trajectory[frame] # advance to frame else: try: frame = u.trajectory.ts.frame except AttributeError: frame = 1 # should catch cases when we are analyzing a single PDB (?) name = name or self.otherargs.get('name', None) if name is None: if number is None: self.number += 1 number = self.number name = "mdanalysis{number:03d}".format(**vars()) # build whole selection in one go (cleaner way to deal with # to deal with line breaks after self.numterms entries) # selection_list must contain entries to be joined with spaces or linebreaks selection_terms = self._translate(selection.atoms) step = self.numterms or len(selection.atoms) out = self._outfile self._write_head(out, name=name) for iatom in range(0, len(selection.atoms), step): line = selection_terms[iatom:iatom + step] out.write(" ".join(line)) if len(line) == step and not iatom + step == len(selection.atoms): out.write(' ' + self.continuation + '\n') out.write(' ') # safe so that we don't have to put a space at the start of tail self._write_tail(out) out.write('\n') # always terminate with newline
def close(self): """Close the file .. versionadded:: 0.16.0 """ self._outfile.close()
[docs] def _translate(self, atoms, **kwargs): """Translate atoms into a list of native selection terms. - build list of ALL selection terms as if this was a single line, e.g. ``['index 12 |', 'index 22 |', 'index 33']`` - only one term per atom!! - terms *must* be strings - something like:: " ".join(terms) must work """ raise NotImplementedError
[docs] def _write_head(self, out, **kwargs): """Initial output to open file object *out*.""" pass # pylint: disable=unnecessary-pass
[docs] def _write_tail(self, out, **kwargs): """Last output to open file object *out*.""" pass # pylint: disable=unnecessary-pass
# Context manager support to match Coordinate writers # all file handles use a with block in their write method, so these do nothing special def __enter__(self): return self def __exit__(self, *exc): self.close()