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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def save_trajs(traj_inp, indexes, prefix='set_', fmt=None, outfiles=None, inmemory=False, stride=1, verbose=False):
 r""" Saves sequences of frames as multiple trajectories. Extracts a number of specified sequences of time/trajectory indexes from the input loader and saves them in a set of molecular dynamics trajectories. The output filenames are obtained by prefix + str(n) + .fmt, where n counts the output trajectory and extension is either set by the user, or else determined from the input. Example: When the input is in dcd format, and indexes is a list of length 3, the output will by default go to files "set_1.dcd", "set_2.dcd", "set_3.dcd". If you want files to be stored in a specific subfolder, simply specify the relative path in the prefix, e.g. prefix='~/macrostates/\pcca_' Parameters traj_inp : :py:class:`pyemma.coordinates.data.feature_reader.FeatureReader` A data source as provided by Please use :py:func:`pyemma.coordinates.source` to construct it. indexes : list of ndarray(T_i, 2) A list of N arrays, each of size (T_n x 2) for writing N trajectories of T_i time steps. Each row contains two indexes (i, t), where i is the index of the trajectory from the input and t is the index of the time step within the trajectory. prefix : str, optional, default = `set_` output filename prefix. Can include an absolute or relative path name. fmt : str, optional, default = None Outpuf file format. By default, the file extension and format. It will be determined from the input. If a different format is desired, specify the corresponding file extension here without a dot, e.g. "dcd" or "xtc". outfiles : list of str, optional, default = None A list of output filenames. When given, this will override the settings of prefix and fmt, and output will be written to these files. inmemory : Boolean, default = False (untested for large files) Instead of internally calling traj_save for every (T_i,2) array in "indexes", only one call is made. Internally, this generates a potentially large molecular trajectory object in memory that is subsequently sliced into the files of "outfiles". Should be faster for large "indexes" arrays and large files, though it is quite memory intensive. The optimal situation is to avoid streaming two times through a huge file for "indexes" of type: indexes = [[1 4000000],[1 4000001]] stride : integer, default is 1 This parameter informs :py:func:`save_trajs` about the stride used in the indexes variable. Typically, the variable indexes contains frame indexes that match exactly the frames of the files contained in traj_inp.trajfiles. However, in certain situations, that might not be the case. Examples of these situations are cases in which stride value != 1 was used when reading/featurizing/transforming/discretizing the files contained in traj_inp.trajfiles. verbose : boolean, default is False Verbose output while looking for "indexes" in the "traj_inp.trajfiles" Returns ------- outfiles : list of str The list of absolute paths that the output files have been written to. """

    # Make sure indexes is iterable
    assert _types.is_iterable(indexes), "Indexes must be an iterable of matrices."
    # only if 2d-array, convert into a list
    if isinstance(indexes, _np.ndarray):
        if indexes.ndim == 2:
            indexes = [indexes]

    # Make sure the elements of that lists are arrays, and that they are shaped properly
    for i_indexes in indexes:
        assert isinstance(i_indexes, _np.ndarray), "The elements in the 'indexes' variable must be numpy.ndarrays"
        assert i_indexes.ndim == 2, \
            "The elements in the 'indexes' variable must have ndim = 2, and not %u" % i_indexes.ndim
        assert i_indexes.shape[1] == 2, \
            "The elements in the 'indexes' variable must be of shape (T_i,2), and not (%u,%u)" % i_indexes.shape

    # Determine output format of the molecular trajectory file
    if fmt is None:
        import os

        _, fmt = os.path.splitext(traj_inp.filenames[0])
    else:
        fmt = '.' + fmt

    # Prepare the list of outfiles before the loop
    if outfiles is None:
        outfiles = []
        for ii in range(len(indexes)):
            outfiles.append(prefix + '%06u' % ii + fmt)

    # Check that we have the same name of outfiles as (T, 2)-indexes arrays
    if len(indexes) != len(outfiles):
        raise Exception('len(indexes) (%s) does not match len(outfiles) (%s)' % (len(indexes), len(outfiles)))

    # This implementation looks for "i_indexes" separately, and thus one traj_inp.trajfile
    # might be accessed more than once (less memory intensive)
    if not inmemory:
        for i_indexes, outfile in zip(indexes, outfiles):
            # TODO: use **kwargs to parse to save_traj
            save_traj(traj_inp, i_indexes, outfile, stride=stride, verbose=verbose)

    # This implementation is "one file - one pass" but might temporally create huge memory objects
    else:
        traj = save_traj(traj_inp, indexes, outfile=None, stride=stride, verbose=verbose)
        i_idx = 0
        for i_indexes, outfile in zip(indexes, outfiles):
            # Create indices for slicing the mdtraj trajectory object
            f_idx = i_idx + len(i_indexes)
            # print i_idx, f_idx
            traj[i_idx:f_idx].save(outfile)
            _logger.info("Created file %s" % outfile)
            # update the initial frame index
            i_idx = f_idx

    return outfiles