Source code for

"""File formats.

This module implements the read(), iread() and write() functions in
For each file format there is an IOFormat object.

There is a dict, ioformats, which stores the objects.


The xyz format is implemented in the ase/io/ file which has a
read_xyz() generator and a write_xyz() function.  This and other
information can be obtained from ioformats['xyz'].

import functools
import inspect
import os
import sys
import warnings
from pathlib import Path, PurePath
from typing import (
    IO, List, Any, Iterable, Tuple, Union, Sequence, Dict, Optional)

from ase.atoms import Atoms
from importlib import import_module
from ase.parallel import parallel_function, parallel_generator

class UnknownFileTypeError(Exception):

class IOFormat:
    def __init__(self, name: str, desc: str, code: str, module_name: str,
                 encoding: str = None) -> None: = name
        self.description = desc
        assert len(code) == 2
        assert code[0] in list('+1')
        assert code[1] in list('BFS')
        self.code = code
        self.module_name = module_name
        self.encoding = encoding

        # (To be set by define_io_format())
        self.extensions: List[str] = []
        self.globs: List[str] = []
        self.magic: List[str] = []

    def open(self, fname, mode: str = 'r') -> IO:
        # We might want append mode, too
        # We can allow more flags as needed (buffering etc.)
        if mode not in list('rwa'):
            raise ValueError("Only modes allowed are 'r', 'w', and 'a'")
        if mode == 'r' and self.can_read:
            raise NotImplementedError('No reader implemented for {} format'
        if mode == 'w' and self.can_write:
            raise NotImplementedError('No writer implemented for {} format'
        if mode == 'a' and not self.can_append:
            raise NotImplementedError('Appending not supported by {} format'

        if self.isbinary:
            mode += 'b'

        path = Path(fname)
        return, encoding=self.encoding)

    def can_read(self) -> bool:
        return is not None

    def can_write(self) -> bool:
        return self.write is not None

    def can_append(self) -> bool:
        return self.can_write and 'append' in self.write.__code__.co_varnames

    def __repr__(self) -> str:
        tokens = ['{}={}'.format(name, repr(value))
                  for name, value in vars(self).items()]
        return 'IOFormat({})'.format(', '.join(tokens))

    def __getitem__(self, i):
        # For compatibility.
        # Historically, the ioformats were listed as tuples
        # with (description, code).  We look like such a tuple.
        return (self.description, self.code)[i]

    def single(self) -> bool:
        """Whether this format is for a single Atoms object."""
        return self.code[0] == '1'

    def _formatname(self) -> str:
        return'-', '_')

    def read(self):
        read = getattr(self.module, 'read_' + self._formatname, None)
        if read and not inspect.isgeneratorfunction(read):
            read = functools.partial(wrap_read_function, read)
        return read

    def write(self):
        return getattr(self.module, 'write_' + self._formatname, None)

    def modes(self) -> str:
        modes = ''
            modes += 'r'
        if self.write:
            modes += 'w'
        return modes

    def full_description(self) -> str:
        lines = ['Name:        {name}',
                 'Description: {description}',
                 'Modes:       {modes}',
                 'Encoding:    {encoding}',
                 'Module:      {module_name}',
                 'Code:        {code}',
                 'Extensions:  {extensions}',
                 'Globs:       {globs}',
                 'Magic:       {magic}']
        desc = '\n'.join(lines)

        myvars = {name: getattr(self, name) for name in dir(self)}
        return desc.format(**myvars)

    def acceptsfd(self) -> bool:
        return self.code[1] != 'S'

    def isbinary(self) -> bool:
        return self.code[1] == 'B'

    def module(self):
        if not self.module_name.startswith(''):
            raise ValueError('Will only import modules from, '
                             'not {}'.format(self.module_name))
            return import_module(self.module_name)
        except ImportError as err:
            raise UnknownFileTypeError('File format not recognized: %s.  '
                                       'Error: %s' % (format, err))

    def match_name(self, basename: str) -> bool:
        from fnmatch import fnmatch
        return any(fnmatch(basename, pattern)
                   for pattern in self.globs)

    def match_magic(self, data: bytes) -> bool:
        # XXX We should use a regex for this!
        from fnmatch import fnmatchcase
        return any(fnmatchcase(data, magic + b'*')  # type: ignore
                   for magic in self.magic)

ioformats: Dict[str, IOFormat] = {}  # These will be filled at run-time.
extension2format = {}

all_formats = ioformats  # Aliased for compatibility only.  Please do not use.
format2modulename = {}  # Left for compatibility only.

def define_io_format(name, desc, code, *, module=None, ext=None,
                     glob=None, magic=None, encoding=None):
    if module is None:
        module = name.replace('-', '_')
        format2modulename[name] = module

    def normalize_patterns(strings):
        if strings is None:
            strings = []
        elif isinstance(strings, (str, bytes)):
            strings = [strings]
            strings = list(strings)
        return strings

    fmt = IOFormat(name, desc, code, module_name='' + module,
    fmt.extensions = normalize_patterns(ext)
    fmt.globs = normalize_patterns(glob)
    fmt.magic = normalize_patterns(magic)

    for ext in fmt.extensions:
        if ext in extension2format:
            raise ValueError('extension "{}" already registered'.format(ext))
        extension2format[ext] = fmt

    ioformats[name] = fmt
    return fmt

def get_ioformat(name: str) -> IOFormat:
    """Return ioformat object or raise appropriate error."""
    if name not in ioformats:
        raise UnknownFileTypeError(name)
    fmt = ioformats[name]
    # Make sure module is importable, since this could also raise an error.
    return ioformats[name]

# We define all the IO formats below.  Each IO format has a code,
# such as '1F', which defines some of the format's properties:
# 1=single atoms object
# +=multiple atoms objects
# F=accepts a file-descriptor
# S=needs a file-name str
# B=like F, but opens in binary mode

F = define_io_format
F('abinit-in', 'ABINIT input file', '1F',
  module='abinit', magic=b'*znucl *'),
F('abinit-out', 'ABINIT output file', '1F',
  module='abinit', magic=b'*.Version * of ABINIT'),
F('aims', 'FHI-aims geometry file', '1S', ext='in'),
F('aims-output', 'FHI-aims output', '+S',
  module='aims', magic=b'*Invoking FHI-aims ...'),
F('bundletrajectory', 'ASE bundle trajectory', '+S'),
F('castep-castep', 'CASTEP output file', '+F',
  module='castep', ext='castep'),
F('castep-cell', 'CASTEP geom file', '1F',
  module='castep', ext='cell'),
F('castep-geom', 'CASTEP trajectory file', '+F',
  module='castep', ext='geom'),
F('castep-md', 'CASTEP molecular dynamics file', '+F',
  module='castep', ext='md'),
F('castep-phonon', 'CASTEP phonon file', '1F',
  module='castep', ext='phonon'),
F('cfg', 'AtomEye configuration', '1F'),
F('cif', 'CIF-file', '+B'),
F('cmdft', 'CMDFT-file', '1F', glob='*I_info'),
F('cp2k-dcd', 'CP2K DCD file', '+B',
  module='cp2k', ext='dcd'),
F('crystal', 'Crystal fort.34 format', '1S',
  ext=['f34', '34'], glob=['f34', '34']),
F('cube', 'CUBE file', '1F'),
F('dacapo-text', 'Dacapo text output', '1F',
  module='dacapo', magic=b'*&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&\n'),
F('db', 'ASE SQLite database file', '+S'),
F('dftb', 'DftbPlus input file', '1S', magic=b'Geometry'),
F('dlp4', 'DL_POLY_4 CONFIG file', '1F',
  module='dlp4', ext='config', glob=['*CONFIG*']),
F('dlp-history', 'DL_POLY HISTORY file', '+F',
  module='dlp4', glob='HISTORY'),
F('dmol-arc', 'DMol3 arc file', '+S',
F('dmol-car', 'DMol3 structure file', '1S',
  module='dmol', ext='car'),
F('dmol-incoor', 'DMol3 structure file', '1S',
F('elk', 'ELK atoms definition', '1S'),
F('eon', 'EON CON file', '+F',
F('eps', 'Encapsulated Postscript', '1S'),
F('espresso-in', 'Quantum espresso in file', '1F',
  module='espresso', ext='pwi', magic=[b'*\n&system', b'*\n&SYSTEM']),
F('espresso-out', 'Quantum espresso out file', '+F',
  module='espresso', ext=['out', 'pwo'], magic=b'*Program PWSCF'),
F('exciting', 'exciting input', '1S', glob='input.xml'),
F('extxyz', 'Extended XYZ file', '+F'),
F('findsym', 'FINDSYM-format', '+F'),
F('gamess-us-out', 'GAMESS-US output file', '1F',
  module='gamess_us', magic=b'*GAMESS')
F('gamess-us-in', 'GAMESS-US input file', '1F',
F('gamess-us-punch', 'GAMESS-US punchcard file', '1F',
  module='gamess_us', magic=b' $DATA', ext='dat')
F('gaussian-in', 'Gaussian com (input) file', '1F',
  module='gaussian', ext=['com', 'gjf']),
F('gaussian-out', 'Gaussian output file', '+F',
  module='gaussian', ext='log', magic=b'*Entering Gaussian System'),
F('acemolecule-out', 'ACE output file', '1S',
F('acemolecule-input', 'ACE input file', '1S',
F('gen', 'DFTBPlus GEN format', '1F'),
F('gif', 'Graphics interchange format', '+S',
F('gpaw-out', 'GPAW text output', '+F',
  magic=b'*  ___ ___ ___ _ _ _'),
F('gpumd', 'GPUMD input file', '1F', glob='')
F('gpw', 'GPAW restart-file', '1S',
  magic=[b'- of UlmGPAW', b'AFFormatGPAW']),
F('gromacs', 'Gromacs coordinates', '1S',
F('gromos', 'Gromos96 geometry file', '1F', ext='g96'),
F('html', 'X3DOM HTML', '1F', module='x3d'),
F('iwm', '?', '1F', glob='atoms.dat'),
F('json', 'ASE JSON database file', '+F', module='db'),
F('jsv', 'JSV file format', '1F'),
F('lammps-dump-text', 'LAMMPS text dump file', '+F',
  module='lammpsrun', magic=b'*\nITEM: TIMESTEP\n'),
F('lammps-dump-binary', 'LAMMPS binary dump file', '+B',
F('lammps-data', 'LAMMPS data file', '1F', module='lammpsdata',
F('magres', 'MAGRES ab initio NMR data file', '1F'),
F('mol', 'MDL Molfile', '1F'),
F('mp4', 'MP4 animation', '+S',
F('mustem', 'muSTEM xtl file', '1F',
F('mysql', 'ASE MySQL database file', '+S',
F('netcdftrajectory', 'AMBER NetCDF trajectory file', '+S'),
F('nomad-json', 'JSON from Nomad archive', '+F',
F('nwchem-in', 'NWChem input file', '1F',
  module='nwchem', ext='nwi'),
F('nwchem-out', 'NWChem output file', '+F',
  module='nwchem', ext='nwo',
  magic=b'*Northwest Computational Chemistry Package'),
F('octopus-in', 'Octopus input file', '1F',
  module='octopus', glob='inp'),
F('proteindatabank', 'Protein Data Bank', '+F',
F('png', 'Portable Network Graphics', '1B'),
F('postgresql', 'ASE PostgreSQL database file', '+S', module='db'),
F('pov', 'Persistance of Vision', '1S'),
# prismatic: Should have ext='xyz' if/when multiple formats can have the same
# extension
F('prismatic', 'prismatic and computem XYZ-file', '1F')
F('py', 'Python file', '+F'),
F('sys', 'qball sys file', '1F'),
F('qbox', 'QBOX output file', '+F',
  magic=b'*:simulation xmlns:'),
F('res', 'SHELX format', '1S', ext='shelx'),
F('rmc6f', 'RMCProfile', '1S', ext='rmc6f'),
F('sdf', 'SDF format', '1F'),
F('struct', 'WIEN2k structure file', '1S', module='wien2k'),
F('struct_out', 'SIESTA STRUCT file', '1F', module='siesta'),
F('traj', 'ASE trajectory', '+B', module='trajectory',
  magic=[b'- of UlmASE-Trajectory', b'AFFormatASE-Trajectory']),
F('trj', 'Old ASE pickle trajectory', '+S',
  module='pickletrajectory', magic=b'PickleTrajectory'),
F('turbomole', 'TURBOMOLE coord file', '1F', glob='coord',
F('turbomole-gradient', 'TURBOMOLE gradient file', '+F',
  module='turbomole', glob='gradient', magic=b'$grad'),
F('v-sim', 'V_Sim ascii file', '1F', ext='ascii'),
F('vasp', 'VASP POSCAR/CONTCAR', '1F',
  ext='poscar', glob=['*POSCAR*', '*CONTCAR*']),
F('vasp-out', 'VASP OUTCAR file', '+F',
  module='vasp', glob='*OUTCAR*'),
F('vasp-xdatcar', 'VASP XDATCAR file', '+F',
  module='vasp', glob='*XDATCAR*'),
F('vasp-xml', 'VASP vasprun.xml file', '+F',
  module='vasp', glob='*vasp*.xml'),
F('vti', 'VTK XML Image Data', '1F', module='vtkxml'),
F('vtu', 'VTK XML Unstructured Grid', '1F', module='vtkxml'),
F('x3d', 'X3D', '1S'),
F('xsd', 'Materials Studio file', '1F'),
F('xsf', 'XCrySDen Structure File', '+F',
  magic=[b'*\nANIMSTEPS', b'*\nCRYSTAL', b'*\nSLAB', b'*\nPOLYMER',
         b'*\nMOLECULE', b'*\nATOMS']),
F('xtd', 'Materials Studio file', '+F'),
F('xyz', 'XYZ-file', '+F')

netcdfconventions2format = {
    '': 'etsf',
    'AMBER': 'netcdftrajectory'

def get_compression(filename: str) -> Tuple[str, Optional[str]]:
    Parse any expected file compression from the extension of a filename.
    Return the filename without the extension, and the extension. Recognises
    ``.gz``, ``.bz2``, ``.xz``.

    >>> get_compression('H2O.pdb.gz')
    ('H2O.pdb', 'gz')
    >>> get_compression('crystal.cif')
    ('crystal.cif', None)

    filename: str
        Full filename including extension.

    (root, extension): (str, str or None)
        Filename split into root without extension, and the extension
        indicating compression format. Will not split if compression
        is not recognised.
    # Update if anything is added
    valid_compression = ['gz', 'bz2', 'xz']

    # Use stdlib as it handles most edge cases
    root, compression = os.path.splitext(filename)

    # extension keeps the '.' so remember to remove it
    if compression.strip('.') in valid_compression:
        return root, compression.strip('.')
        return filename, None

def open_with_compression(filename: str, mode: str = 'r') -> IO:
    Wrapper around builtin `open` that will guess compression of a file
    from the filename and open it for reading or writing as if it were
    a standard file.

    Implemented for ``gz``(gzip), ``bz2``(bzip2) and ``xz``(lzma).

    Supported modes are:
       * 'r', 'rt', 'w', 'wt' for text mode read and write.
       * 'rb, 'wb' for binary read and write.

    filename: str
        Path to the file to open, including any extensions that indicate
        the compression used.
    mode: str
        Mode to open the file, same as for builtin ``open``, e.g 'r', 'w'.

    fd: file
        File-like object open with the specified mode.

    # Compressed formats sometimes default to binary, so force text mode.
    if mode == 'r':
        mode = 'rt'
    elif mode == 'w':
        mode = 'wt'
    elif mode == 'a':
        mode = 'at'

    root, compression = get_compression(filename)

    if compression is None:
        return open(filename, mode)
    elif compression == 'gz':
        import gzip
        fd =, mode=mode)
    elif compression == 'bz2':
        import bz2
        fd =, mode=mode)
    elif compression == 'xz':
        import lzma
        fd =, mode)
        fd = open(filename, mode)

    return fd

def wrap_read_function(read, filename, index=None, **kwargs):
    """Convert read-function to generator."""
    if index is None:
        yield read(filename, **kwargs)
        for atoms in read(filename, index, **kwargs):
            yield atoms

NameOrFile = Union[str, PurePath, IO]

[docs]def write( filename: NameOrFile, images: Union[Atoms, Sequence[Atoms]], format: str = None, parallel: bool = True, append: bool = False, **kwargs: dict ) -> None: """Write Atoms object(s) to file. filename: str or file Name of the file to write to or a file descriptor. The name '-' means standard output. images: Atoms object or list of Atoms objects A single Atoms object or a list of Atoms objects. format: str Used to specify the file-format. If not given, the file-format will be taken from suffix of the filename. parallel: bool Default is to write on master only. Use parallel=False to write from all slaves. append: bool Default is to open files in 'w' or 'wb' mode, overwriting existing files. In some cases opening the file in 'a' or 'ab' mode (appending) is useful, e.g. writing trajectories or saving multiple Atoms objects in one file. WARNING: If the file format does not support multiple entries without additional keywords/headers, files created using 'append=True' might not be readable by any program! They will nevertheless be written without error message. The use of additional keywords is format specific.""" if isinstance(filename, PurePath): filename = str(filename) if isinstance(filename, str): filename = os.path.expanduser(filename) fd = None if filename == '-': fd = sys.stdout filename = None # type: ignore elif format is None: format = filetype(filename, read=False) assert isinstance(format, str) else: fd = filename # type: ignore filename = None # type: ignore format = format or 'json' # default is json io = get_ioformat(format) _write(filename, fd, format, io, images, parallel=parallel, append=append, **kwargs)
@parallel_function def _write(filename, fd, format, io, images, parallel=None, append=False, **kwargs): if isinstance(images, Atoms): images = [images] if io.single: if len(images) > 1: raise ValueError('{}-format can only store 1 Atoms object.' .format(format)) images = images[0] if io.write is None: raise ValueError("Can't write to {}-format".format(format)) # Special case for json-format: if format == 'json' and (len(images) > 1 or append): if filename is not None: io.write(filename, images, append=append, **kwargs) return raise ValueError("Can't write more than one image to file-descriptor " 'using json-format.') if io.acceptsfd: open_new = (fd is None) if open_new: mode = 'wb' if io.isbinary else 'w' if append: mode = mode.replace('w', 'a') fd = open_with_compression(filename, mode) # XXX remember to re-enable compressed open # fd =, mode) io.write(fd, images, **kwargs) if open_new: fd.close() else: if fd is not None: raise ValueError("Can't write {}-format to file-descriptor" .format(format)) if io.can_append: io.write(filename, images, append=append, **kwargs) elif append: raise ValueError("Cannot append to {}-format, write-function " "does not support the append keyword." .format(format)) else: io.write(filename, images, **kwargs)
[docs]def read( filename: NameOrFile, index: Any = None, format: str = None, parallel: bool = True, do_not_split_by_at_sign: bool = False, **kwargs ) -> Union[Atoms, List[Atoms]]: """Read Atoms object(s) from file. filename: str or file Name of the file to read from or a file descriptor. index: int, slice or str The last configuration will be returned by default. Examples: * ``index=0``: first configuration * ``index=-2``: second to last * ``index=':'`` or ``index=slice(None)``: all * ``index='-3:'`` or ``index=slice(-3, None)``: three last * ``index='::2'`` or ``index=slice(0, None, 2)``: even * ``index='1::2'`` or ``index=slice(1, None, 2)``: odd format: str Used to specify the file-format. If not given, the file-format will be guessed by the *filetype* function. parallel: bool Default is to read on master and broadcast to slaves. Use parallel=False to read on all slaves. do_not_split_by_at_sign: bool If False (default) ``filename`` is splited by at sign ``@`` Many formats allow on open file-like object to be passed instead of ``filename``. In this case the format cannot be auto-decected, so the ``format`` argument should be explicitly given.""" if isinstance(filename, PurePath): filename = str(filename) if filename == '-': filename = sys.stdin if isinstance(index, str): try: index = string2index(index) except ValueError: pass filename, index = parse_filename(filename, index, do_not_split_by_at_sign) if index is None: index = -1 format = format or filetype(filename) io = get_ioformat(format) if isinstance(index, (slice, str)): return list(_iread(filename, index, format, io, parallel=parallel, **kwargs)) else: return next(_iread(filename, slice(index, None), format, io, parallel=parallel, **kwargs))
[docs]def iread( filename: NameOrFile, index: Any = None, format: str = None, parallel: bool = True, do_not_split_by_at_sign: bool = False, **kwargs ) -> Iterable[Atoms]: """Iterator for reading Atoms objects from file. Works as the `read` function, but yields one Atoms object at a time instead of all at once.""" if isinstance(filename, PurePath): filename = str(filename) if isinstance(index, str): index = string2index(index) filename, index = parse_filename(filename, index, do_not_split_by_at_sign) if index is None or index == ':': index = slice(None, None, None) if not isinstance(index, (slice, str)): index = slice(index, (index + 1) or None) format = format or filetype(filename) io = get_ioformat(format) for atoms in _iread(filename, index, format, io, parallel=parallel, **kwargs): yield atoms
@parallel_generator def _iread(filename, index, format, io, parallel=None, full_output=False, **kwargs): if isinstance(filename, str): filename = os.path.expanduser(filename) if not raise ValueError("Can't read from {}-format".format(format)) if io.single: start = index.start assert start is None or start == 0 or start == -1 args = () else: args = (index,) must_close_fd = False if isinstance(filename, str): if io.acceptsfd: mode = 'rb' if io.isbinary else 'r' fd = open_with_compression(filename, mode) must_close_fd = True else: fd = filename else: assert io.acceptsfd fd = filename # Make sure fd is closed in case loop doesn't finish: try: for dct in, *args, **kwargs): if not isinstance(dct, dict): dct = {'atoms': dct} if full_output: yield dct else: yield dct['atoms'] finally: if must_close_fd: fd.close() def parse_filename(filename, index=None, do_not_split_by_at_sign=False): if not isinstance(filename, str): return filename, index basename = os.path.basename(filename) if do_not_split_by_at_sign or '@' not in basename: return filename, index newindex = None newfilename, newindex = filename.rsplit('@', 1) if isinstance(index, slice): return newfilename, index try: newindex = string2index(newindex) except ValueError: warnings.warn('Can not parse index for path \n' ' "%s" \nConsider set ' 'do_not_split_by_at_sign=True \nif ' 'there is no index.' % filename) return newfilename, newindex def string2index(string: str) -> Union[int, slice, str]: """Convert index string to either int or slice""" if ':' not in string: # may contain database accessor try: return int(string) except ValueError: return string i: List[Optional[int]] = [] for s in string.split(':'): if s == '': i.append(None) else: i.append(int(s)) i += (3 - len(i)) * [None] return slice(*i) def filetype( filename: NameOrFile, read: bool = True, guess: bool = True, ) -> str: """Try to guess the type of the file. First, special signatures in the filename will be checked for. If that does not identify the file type, then the first 2000 bytes of the file will be read and analysed. Turn off this second part by using read=False. Can be used from the command-line also:: $ ase info filename ... """ ext = None if isinstance(filename, str): if os.path.isdir(filename): if os.path.basename(os.path.normpath(filename)) == 'states': return 'eon' return 'bundletrajectory' if filename.startswith('postgres'): return 'postgresql' if filename.startswith('mysql') or filename.startswith('mariadb'): return 'mysql' # strip any compression extensions that can be read root, compression = get_compression(filename) basename = os.path.basename(root) if '.' in basename: ext = os.path.splitext(basename)[1].strip('.').lower() if ext in ['xyz', 'cube', 'json', 'cif']: return ext for fmt in ioformats.values(): if fmt.match_name(basename): return if not read: if ext is None: raise UnknownFileTypeError('Could not guess file type') ioformat = extension2format.get(ext) if ioformat: return # askhl: This is strange, we don't know if ext is a format: return ext fd = open_with_compression(filename, 'rb') else: fd = filename # type: ignore if fd is sys.stdin: return 'json' data = if fd is not filename: fd.close() else: if len(data) == 0: raise UnknownFileTypeError('Empty file: ' + filename) # type: ignore if data.startswith(b'CDF'): # We can only recognize these if we actually have the netCDF4 module. try: import netCDF4 except ImportError: pass else: nc = netCDF4.Dataset(filename) if 'Conventions' in nc.ncattrs(): if nc.Conventions in netcdfconventions2format: return netcdfconventions2format[nc.Conventions] else: raise UnknownFileTypeError( "Unsupported NetCDF convention: " "'{}'".format(nc.Conventions)) else: raise UnknownFileTypeError("NetCDF file does not have a " "'Conventions' attribute.") for ioformat in ioformats.values(): if ioformat.match_magic(data): return format = None if ext in extension2format: format = extension2format[ext].name if format is None and guess: format = ext if format is None: # Do quick xyz check: lines = data.splitlines() if lines and lines[0].strip().isdigit(): return 'xyz' raise UnknownFileTypeError('Could not guess file type') assert isinstance(format, str) return format def index2range(index, nsteps): """Method to convert a user given *index* option to a list of indices. Returns a range. """ if isinstance(index, int): if index < 0: tmpsnp = nsteps + index trbl = range(tmpsnp, tmpsnp + 1, 1) else: trbl = range(index, index + 1, 1) elif isinstance(index, slice): start = index.start stop = index.stop step = index.step if start is None: start = 0 elif start < 0: start = nsteps + start if step is None: step = 1 if stop is None: stop = nsteps elif stop < 0: stop = nsteps + stop trbl = range(start, stop, step) else: raise RuntimeError("index2range handles integers and slices only.") return trbl