def find_sink_reactions(model):
    u"""
    Return a list of sink reactions.

    Parameters
    ----------
    model : cobra.Model
        The metabolic model under investigation.

    Notes
    -----
    [1] defines sink reactions as:
    -- 'similar to demand reactions' but reversible, thus able to supply the
    model with metabolites
    -- reactions that are chiefly added during the gap-filling process
    -- as a means of dealing with 'compounds that are produced by nonmetabolic
    cellular processes but that need to be metabolized'
    -- reactions with a formula such as: 'met_c <-> '

    Sink reactions differ from exchange reactions in that the metabolites
    are not removed from the extracellular environment, but from any of the
    organism's compartments.

    References
    ----------
    .. [1] Thiele, I., & Palsson, B. Ø. (2010, January). A protocol for
           generating a high-quality genome-scale metabolic reconstruction.
           Nature protocols. Nature Publishing Group.
           http://doi.org/10.1038/nprot.2009.203

    """
    try:
        extracellular = find_compartment_id_in_model(model, 'e')
    except KeyError:
        extracellular = None
    return find_boundary_types(model, 'sink', extracellular)
u"""
    Return a list of sink reactions.

    Parameters
    ----------
    model : cobra.Model
        The metabolic model under investigation.

    Notes
    -----
    [1] defines sink reactions as:
    -- 'similar to demand reactions' but reversible, thus able to supply the
    model with metabolites
    -- reactions that are chiefly added during the gap-filling process
    -- as a means of dealing with 'compounds that are produced by nonmetabolic
    cellular processes but that need to be metabolized'
    -- reactions with a formula such as: 'met_c <-> '

    Sink reactions differ from exchange reactions in that the metabolites
    are not removed from the extracellular environment, but from any of the
    organism's compartments.

    References
    ----------
    .. [1] Thiele, I., & Palsson, B. Ø. (2010, January). A protocol for
           generating a high-quality genome-scale metabolic reconstruction.
           Nature protocols. Nature Publishing Group.
           http://doi.org/10.1038/nprot.2009.203