def true_num_reactions(model, custom_spont_id=None):
    """Return the number of reactions associated with a gene.

    Args:
        model (Model):
        custom_spont_id (str): Optional custom spontaneous ID if it does not match the regular expression ``[Ss](_|)0001``

    Returns:
        int: Number of reactions associated with a gene

    """
    true_num = 0
    for rxn in model.reactions:
        if len(rxn.genes) == 0:
            continue
        if len(rxn.genes) == 1 and is_spontaneous(list(rxn.genes)[0], custom_id=custom_spont_id):
            continue
        else:
            true_num += 1
    return true_num
Return the number of reactions associated with a gene.

    Args:
        model (Model):
        custom_spont_id (str): Optional custom spontaneous ID if it does not match the regular expression ``[Ss](_|)0001``

    Returns:
        int: Number of reactions associated with a gene