Example #1
0
def get_libsbml_document(cobra_model,
                         sbml_level=2,
                         sbml_version=1,
                         print_time=False,
                         use_fbc_package=True):
    """ Return a libsbml document object for writing to a file. This function
    is used by write_cobra_model_to_sbml_file(). """

    note_start_tag, note_end_tag = '<p>', '</p>'
    if sbml_level > 2 or (sbml_level == 2 and sbml_version == 4):
        note_start_tag, note_end_tag = '<html:p>', '</html:p>'

    sbml_doc = SBMLDocument(sbml_level, sbml_version)
    sbml_model = sbml_doc.createModel(cobra_model.id.split('.')[0])
    #Note need to set units
    reaction_units = 'mmol_per_gDW_per_hr'
    model_units = sbml_model.createUnitDefinition()
    model_units.setId(reaction_units)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_MOLE)
    sbml_unit.setScale(-3)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_GRAM)
    sbml_unit.setExponent(-1)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_SECOND)
    sbml_unit.setMultiplier(1.0 / 60 / 60)
    sbml_unit.setExponent(-1)

    #Add in the common compartment abbreviations.  If there are additional compartments
    #they also need to be added.
    if not cobra_model.compartments:
        cobra_model.compartments = {
            'c': 'cytosol',
            'p': 'periplasm',
            'e': 'extracellular'
        }
    for the_key in cobra_model.compartments.keys():
        sbml_comp = sbml_model.createCompartment()
        sbml_comp.setId(the_key)
        sbml_comp.setName(cobra_model.compartments[the_key])
        sbml_comp.setSize(1)  #Just to get rid of warnings

    if print_time:
        warn("print_time is deprecated")
    #Use this dict to allow for fast look up of species id
    #for references created in the reaction section.
    metabolite_dict = {}

    for cobra_metabolite in cobra_model.metabolites:
        metabolite_dict[cobra_metabolite.id] = add_sbml_species(
            sbml_model,
            cobra_metabolite,
            note_start_tag=note_start_tag,
            note_end_tag=note_end_tag)

    for the_reaction in cobra_model.reactions:
        #This is probably the culprit.  Including cobra.Reaction
        #objects explicitly in cobra.Model will speed this up.
        sbml_reaction = sbml_model.createReaction()
        #Need to remove - for proper SBML.  Replace with __
        the_reaction_id = 'R_' + the_reaction.id.replace('-', '__')
        sbml_reaction.setId(the_reaction_id)
        # The reason we are not using the Reaction.reversibility property
        # is because the SBML definition of reversibility does not quite
        # match with the cobra definition. In cobra, reversibility implies
        # that both positive and negative flux values are feasible. However,
        # SBML requires negative-flux-only reactions to still be classified
        # as reversible. To quote from the SBML Level 3 Version 1 Spec:
        # > However, labeling a reaction as irreversible is interpreted as
        # > an assertion that the rate expression will not have negative
        # > values during a simulation.
        # (Page 60 lines 44-45)
        sbml_reaction.setReversible(the_reaction.lower_bound < 0)
        if the_reaction.name:
            sbml_reaction.setName(the_reaction.name)
        else:
            sbml_reaction.setName(the_reaction.id)
        #Add in the reactant/product references
        for the_metabolite, the_coefficient in the_reaction._metabolites.items(
        ):
            sbml_stoichiometry = the_coefficient
            metabolite_id = str(metabolite_dict[the_metabolite.id])
            #Each SpeciesReference must have a unique id
            if sbml_stoichiometry < 0:
                species_reference = sbml_reaction.createReactant()
            else:
                species_reference = sbml_reaction.createProduct()
            species_reference.setId(metabolite_id + '_' + the_reaction_id)
            species_reference.setSpecies(metabolite_id)
            species_reference.setStoichiometry(abs(sbml_stoichiometry))
        #Deal with the case where the reaction is a boundary reaction
        if len(the_reaction._metabolites) == 1:
            the_metabolite, the_coefficient = list(
                the_reaction._metabolites.items())[0]
            metabolite_id = add_sbml_species(sbml_model,
                                             the_metabolite,
                                             note_start_tag=note_start_tag,
                                             note_end_tag=note_end_tag,
                                             boundary_metabolite=True)
            sbml_stoichiometry = -the_coefficient
            #Each SpeciesReference must have a unique id
            if sbml_stoichiometry < 0:
                species_reference = sbml_reaction.createReactant()
            else:
                species_reference = sbml_reaction.createProduct()
            species_reference.setId(metabolite_id + '_' + the_reaction_id)
            species_reference.setSpecies(metabolite_id)
            species_reference.setStoichiometry(abs(sbml_stoichiometry))

        #Add in the kineticLaw
        sbml_law = KineticLaw(sbml_level, sbml_version)
        if hasattr(sbml_law, 'setId'):
            sbml_law.setId('FLUX_VALUE')
        sbml_law.setFormula('FLUX_VALUE')
        reaction_parameter_dict = {
            'LOWER_BOUND': [the_reaction.lower_bound, reaction_units],
            'UPPER_BOUND': [the_reaction.upper_bound, reaction_units],
            'FLUX_VALUE': [0, reaction_units],
            'OBJECTIVE_COEFFICIENT':
            [the_reaction.objective_coefficient, 'dimensionless']
        }
        for k, v in reaction_parameter_dict.items():
            sbml_parameter = Parameter(sbml_level, sbml_version)
            sbml_parameter.setId(k)
            if hasattr(v, '__iter__'):
                sbml_parameter.setValue(v[0])
                sbml_parameter.setUnits(v[1])
            else:
                sbml_parameter.setValue(v)
            sbml_law.addParameter(sbml_parameter)
        sbml_reaction.setKineticLaw(sbml_law)

        #Checks if GPR and Subsystem annotations are present in the notes section and if they are the same as those in
        #the reaction's gene_reaction_rule/ subsystem attribute
        #If they are not identical, they are set to be identical
        note_dict = the_reaction.notes.copy()
        if the_reaction.gene_reaction_rule:
            if 'GENE ASSOCIATION' in note_dict:
                del note_dict['GENE ASSOCIATION']
            note_dict['GENE_ASSOCIATION'] = [
                str(the_reaction.gene_reaction_rule)
            ]
        if the_reaction.subsystem:
            note_dict['SUBSYSTEM'] = [str(the_reaction.subsystem)]

        #In a cobrapy model the notes section is stored as a dictionary. The following section turns the key-value-pairs
        #of the dictionary into a string and replaces recurring symbols so that the string has the required syntax for
        #an SBML doc.
        note_str = str(list(iteritems(note_dict)))
        note_start_tag, note_end_tag, note_delimiter = '<p>', '</p>', ':'
        note_str = note_str.replace('(\'', note_start_tag)
        note_str = note_str.replace('\']),', note_end_tag)
        note_str = note_str.replace('\',', note_delimiter)
        note_str = note_str.replace('\']', '')
        note_str = note_str.replace('[\'', '')
        note_str = note_str.replace(
            '[', '<html xmlns="http://www.w3.org/1999/xhtml">')
        note_str = note_str.replace(')]', note_end_tag + '</html>')
        sbml_reaction.setNotes(note_str)

    if use_fbc_package:
        try:
            from libsbml import ConversionProperties, LIBSBML_OPERATION_SUCCESS
            conversion_properties = ConversionProperties()
            conversion_properties.addOption("convert cobra", True,
                                            "Convert Cobra model")
            result = sbml_doc.convert(conversion_properties)
            if result != LIBSBML_OPERATION_SUCCESS:
                raise Exception("Conversion of COBRA to SBML+fbc failed")
        except Exception as e:
            error_string = 'Error saving as SBML+fbc. %s'
            try:
                #Check whether the FbcExtension is there
                from libsbml import FbcExtension
                error_string = error_string % e
            except ImportError:
                error_string = error_string%'FbcExtension not available in libsbml. ' +\
                               'If use_fbc_package == True then libsbml must be compiled with ' +\
                               'the fbc extension. '
                from libsbml import getLibSBMLDottedVersion
                _sbml_version = getLibSBMLDottedVersion()
                _major, _minor, _patch = map(int, _sbml_version.split('.'))
                if _major < 5 or (_major == 5 and _minor < 8):
                    error_string += "You've got libsbml %s installed.   You need 5.8.0 or later with the fbc package"

            raise (Exception(error_string))
    return sbml_doc
Example #2
0
def get_libsbml_document(cobra_model,
                                   sbml_level=2, sbml_version=1,
                                   print_time=False,
                                   use_fbc_package=True):

    """ Return a libsbml document object for writing to a file. This function
    is used by write_cobra_model_to_sbml_file(). """

    note_start_tag, note_end_tag = '<p>', '</p>'
    if sbml_level > 2 or (sbml_level == 2 and sbml_version == 4):
        note_start_tag, note_end_tag = '<html:p>', '</html:p>'
        
    
    sbml_doc = SBMLDocument(sbml_level, sbml_version)
    sbml_model = sbml_doc.createModel(cobra_model.id.split('.')[0])
    #Note need to set units
    reaction_units = 'mmol_per_gDW_per_hr'
    model_units = sbml_model.createUnitDefinition()
    model_units.setId(reaction_units)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_MOLE)
    sbml_unit.setScale(-3)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_GRAM)
    sbml_unit.setExponent(-1)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_SECOND)
    sbml_unit.setMultiplier(1.0/60/60)
    sbml_unit.setExponent(-1)

    #Add in the common compartment abbreviations.  If there are additional compartments
    #they also need to be added.
    if not cobra_model.compartments:
        cobra_model.compartments = {'c': 'cytosol',
                                    'p': 'periplasm',
                                    'e': 'extracellular'}    
    for the_key in cobra_model.compartments.keys():
        sbml_comp = sbml_model.createCompartment()
        sbml_comp.setId(the_key)
        sbml_comp.setName(cobra_model.compartments[the_key])
        sbml_comp.setSize(1) #Just to get rid of warnings

    if print_time:
        warn("print_time is deprecated")
    #Use this dict to allow for fast look up of species id
    #for references created in the reaction section.
    metabolite_dict = {}

    for cobra_metabolite in cobra_model.metabolites:
        metabolite_dict[cobra_metabolite.id] =  add_sbml_species(sbml_model,
                                                                 cobra_metabolite,
                                                                 note_start_tag=note_start_tag,
                                                                 note_end_tag=note_end_tag)

    for the_reaction in cobra_model.reactions:
        #This is probably the culprit.  Including cobra.Reaction
        #objects explicitly in cobra.Model will speed this up.
        sbml_reaction = sbml_model.createReaction()
        #Need to remove - for proper SBML.  Replace with __
        the_reaction_id = 'R_' + the_reaction.id.replace('-','__' )
        sbml_reaction.setId(the_reaction_id)
        # The reason we are not using the Reaction.reversibility property
        # is because the SBML definition of reversibility does not quite
        # match with the cobra definition. In cobra, reversibility implies
        # that both positive and negative flux values are feasible. However,
        # SBML requires negative-flux-only reactions to still be classified
        # as reversible. To quote from the SBML Level 3 Version 1 Spec:
        # > However, labeling a reaction as irreversible is interpreted as
        # > an assertion that the rate expression will not have negative
        # > values during a simulation.
        # (Page 60 lines 44-45)
        sbml_reaction.setReversible(the_reaction.lower_bound < 0)
        if the_reaction.name:
            sbml_reaction.setName(the_reaction.name)
        else:
            sbml_reaction.setName(the_reaction.id)
        #Add in the reactant/product references
        for the_metabolite, the_coefficient in the_reaction._metabolites.items():
            sbml_stoichiometry = the_coefficient
            metabolite_id = str(metabolite_dict[the_metabolite.id])
            #Each SpeciesReference must have a unique id
            if sbml_stoichiometry < 0:
                species_reference = sbml_reaction.createReactant()
            else:
                species_reference = sbml_reaction.createProduct()
            species_reference.setId(metabolite_id + '_' + the_reaction_id)
            species_reference.setSpecies(metabolite_id)
            species_reference.setStoichiometry(abs(sbml_stoichiometry))
        #Deal with the case where the reaction is a boundary reaction
        if len(the_reaction._metabolites) == 1:
            the_metabolite, the_coefficient = list(the_reaction._metabolites.items())[0]
            metabolite_id = add_sbml_species(sbml_model, the_metabolite,
                                             note_start_tag=note_start_tag,
                                             note_end_tag=note_end_tag,
                                             boundary_metabolite=True)
            sbml_stoichiometry = -the_coefficient
            #Each SpeciesReference must have a unique id
            if sbml_stoichiometry < 0:
                species_reference = sbml_reaction.createReactant()
            else:
                species_reference = sbml_reaction.createProduct()
            species_reference.setId(metabolite_id + '_' + the_reaction_id)
            species_reference.setSpecies(metabolite_id)
            species_reference.setStoichiometry(abs(sbml_stoichiometry))
            
        #Add in the kineticLaw
        sbml_law = KineticLaw(sbml_level, sbml_version)
        if hasattr(sbml_law, 'setId'):
            sbml_law.setId('FLUX_VALUE')
        sbml_law.setFormula('FLUX_VALUE')
        reaction_parameter_dict = {'LOWER_BOUND': [the_reaction.lower_bound, reaction_units],
                                   'UPPER_BOUND': [the_reaction.upper_bound, reaction_units],
                                   'FLUX_VALUE': [0, reaction_units],
                                   'OBJECTIVE_COEFFICIENT': [the_reaction.objective_coefficient,
                                                             'dimensionless']}
        for k, v in reaction_parameter_dict.items():
            sbml_parameter = Parameter(sbml_level, sbml_version)
            sbml_parameter.setId(k)
            if hasattr(v, '__iter__'):
                sbml_parameter.setValue(v[0])
                sbml_parameter.setUnits(v[1])
            else:
                sbml_parameter.setValue(v)
            sbml_law.addParameter(sbml_parameter)
        sbml_reaction.setKineticLaw(sbml_law)

        #Checks if GPR and Subsystem annotations are present in the notes section and if they are the same as those in
        #the reaction's gene_reaction_rule/ subsystem attribute
        #If they are not identical, they are set to be identical
        note_dict = the_reaction.notes.copy()
        if the_reaction.gene_reaction_rule:
            note_dict['GENE_ASSOCIATION'] = [str(the_reaction.gene_reaction_rule)]
        if the_reaction.subsystem:
            note_dict['SUBSYSTEM'] = [str(the_reaction.subsystem)]

        #In a cobrapy model the notes section is stored as a dictionary. The following section turns the key-value-pairs
        #of the dictionary into a string and replaces recurring symbols so that the string has the required syntax for
        #an SBML doc.
        note_str = str(list(iteritems(note_dict)))
        note_start_tag, note_end_tag, note_delimiter = '<p>', '</p>', ':'
        note_str = note_str.replace('(\'',note_start_tag)
        note_str = note_str.replace('\']),',note_end_tag)
        note_str = note_str.replace('\',',note_delimiter)
        note_str = note_str.replace('\']','')
        note_str = note_str.replace('[\'','')
        note_str = note_str.replace('[','<html xmlns="http://www.w3.org/1999/xhtml">')
        note_str = note_str.replace(')]',note_end_tag+'</html>')
        sbml_reaction.setNotes(note_str)

    if use_fbc_package:
        try:
            from libsbml import ConversionProperties, LIBSBML_OPERATION_SUCCESS
            conversion_properties = ConversionProperties()
            conversion_properties.addOption("convert cobra", True, "Convert Cobra model")
            result = sbml_doc.convert(conversion_properties)
            if result != LIBSBML_OPERATION_SUCCESS:
                raise Exception("Conversion of COBRA to SBML+fbc failed")
        except Exception as e:
            error_string = 'Error saving as SBML+fbc. %s'
            try:
                #Check whether the FbcExtension is there
                from libsbml import FbcExtension
                error_string = error_string%e
            except ImportError:
                error_string = error_string%'FbcExtension not available in libsbml. ' +\
                               'If use_fbc_package == True then libsbml must be compiled with ' +\
                               'the fbc extension. '
                from libsbml import getLibSBMLDottedVersion
                _sbml_version = getLibSBMLDottedVersion()
                _major, _minor, _patch = map(int, _sbml_version.split('.'))
                if _major < 5 or (_major == 5 and _minor < 8):
                    error_string += "You've got libsbml %s installed.   You need 5.8.0 or later with the fbc package"

            raise(Exception(error_string))
    return sbml_doc
Example #3
0
def write_cobra_model_to_sbml_file(cobra_model,
                                   sbml_filename,
                                   sbml_level=2,
                                   sbml_version=1,
                                   print_time=False,
                                   use_fbc_package=True):
    """Write a cobra.Model object to an SBML XML file.

    cobra_model:  :class:`~cobra.core.Model.Model` object

    sbml_filename:  The file to write the SBML XML to.

    sbml_level:  2 is the only level supported at the moment.

    sbml_version: 1 is the only version supported at the moment.

    use_fbc_package: Boolean.
        Convert the model to the FBC package format to improve portability.
        http://sbml.org/Documents/Specifications/SBML_Level_3/Packages/Flux_Balance_Constraints_(flux)


    TODO: Update the NOTES to match the SBML standard and provide support for
    Level 2 Version 4

    """
    note_start_tag, note_end_tag = '<p>', '</p>'
    if sbml_level > 2 or (sbml_level == 2 and sbml_version == 4):
        note_start_tag, note_end_tag = '<html:p>', '</html:p>'

    sbml_doc = SBMLDocument(sbml_level, sbml_version)
    sbml_model = sbml_doc.createModel(cobra_model.id.split('.')[0])
    #Note need to set units
    reaction_units = 'mmol_per_gDW_per_hr'
    model_units = sbml_model.createUnitDefinition()
    model_units.setId(reaction_units)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_MOLE)
    sbml_unit.setScale(-3)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_GRAM)
    sbml_unit.setExponent(-1)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_SECOND)
    sbml_unit.setMultiplier(1.0 / 60 / 60)
    sbml_unit.setExponent(-1)

    #Add in the common compartment abbreviations.  If there are additional compartments
    #they also need to be added.
    if not cobra_model.compartments:
        cobra_model.compartments = {
            'c': 'cytosol',
            'p': 'periplasm',
            'e': 'extracellular'
        }
    for the_key in cobra_model.compartments.keys():
        sbml_comp = sbml_model.createCompartment()
        sbml_comp.setId(the_key)
        sbml_comp.setName(cobra_model.compartments[the_key])
        sbml_comp.setSize(1)  #Just to get rid of warnings

    if print_time:
        warn("print_time is deprecated")
    #Use this dict to allow for fast look up of species id
    #for references created in the reaction section.
    metabolite_dict = {}

    for cobra_metabolite in cobra_model.metabolites:
        metabolite_dict[cobra_metabolite.id] = add_sbml_species(
            sbml_model,
            cobra_metabolite,
            note_start_tag=note_start_tag,
            note_end_tag=note_end_tag)

    for the_reaction in cobra_model.reactions:
        #This is probably the culprit.  Including cobra.Reaction
        #objects explicitly in cobra.Model will speed this up.
        sbml_reaction = sbml_model.createReaction()
        #Need to remove - for proper SBML.  Replace with __
        the_reaction_id = 'R_' + the_reaction.id.replace('-', '__')
        sbml_reaction.setId(the_reaction_id)
        # The reason we are not using the Reaction.reversibility property
        # is because the SBML definition of reversibility does not quite
        # match with the cobra definition. In cobra, reversibility implies
        # that both positive and negative flux values are feasible. However,
        # SBML requires negative-flux-only reactions to still be classified
        # as reversible. To quote from the SBML Level 3 Version 1 Spec:
        # > However, labeling a reaction as irreversible is interpreted as
        # > an assertion that the rate expression will not have negative
        # > values during a simulation.
        # (Page 60 lines 44-45)
        sbml_reaction.setReversible(the_reaction.lower_bound < 0)
        if the_reaction.name:
            sbml_reaction.setName(the_reaction.name)
        else:
            sbml_reaction.setName(the_reaction.id)
        #Add in the reactant/product references
        for the_metabolite, the_coefficient in the_reaction._metabolites.items(
        ):
            sbml_stoichiometry = the_coefficient
            metabolite_id = str(metabolite_dict[the_metabolite.id])
            #Each SpeciesReference must have a unique id
            if sbml_stoichiometry < 0:
                species_reference = sbml_reaction.createReactant()
            else:
                species_reference = sbml_reaction.createProduct()
            species_reference.setId(metabolite_id + '_' + the_reaction_id)
            species_reference.setSpecies(metabolite_id)
            species_reference.setStoichiometry(abs(sbml_stoichiometry))
        #Deal with the case where the reaction is a boundary reaction
        if len(the_reaction._metabolites) == 1:
            the_metabolite, the_coefficient = list(
                the_reaction._metabolites.items())[0]
            metabolite_id = add_sbml_species(sbml_model,
                                             the_metabolite,
                                             note_start_tag=note_start_tag,
                                             note_end_tag=note_end_tag,
                                             boundary_metabolite=True)
            sbml_stoichiometry = -the_coefficient
            #Each SpeciesReference must have a unique id
            if sbml_stoichiometry < 0:
                species_reference = sbml_reaction.createReactant()
            else:
                species_reference = sbml_reaction.createProduct()
            species_reference.setId(metabolite_id + '_' + the_reaction_id)
            species_reference.setSpecies(metabolite_id)
            species_reference.setStoichiometry(abs(sbml_stoichiometry))

        #Add in the kineticLaw
        sbml_law = KineticLaw(sbml_level, sbml_version)
        if hasattr(sbml_law, 'setId'):
            sbml_law.setId('FLUX_VALUE')
        sbml_law.setFormula('FLUX_VALUE')
        reaction_parameter_dict = {
            'LOWER_BOUND': [the_reaction.lower_bound, reaction_units],
            'UPPER_BOUND': [the_reaction.upper_bound, reaction_units],
            'FLUX_VALUE': [0, reaction_units],
            'OBJECTIVE_COEFFICIENT':
            [the_reaction.objective_coefficient, 'dimensionless']
        }
        for k, v in reaction_parameter_dict.items():
            sbml_parameter = Parameter(sbml_level, sbml_version)
            sbml_parameter.setId(k)
            if hasattr(v, '__iter__'):
                sbml_parameter.setValue(v[0])
                sbml_parameter.setUnits(v[1])
            else:
                sbml_parameter.setValue(v)
            sbml_law.addParameter(sbml_parameter)
        sbml_reaction.setKineticLaw(sbml_law)
        sbml_reaction.setNotes(
            '<html xmlns="http://www.w3.org/1999/xhtml">%sGENE_ASSOCIATION: %s%s%sSUBSYSTEM: %s%s</html>'
            % (note_start_tag, the_reaction.gene_reaction_rule, note_end_tag,
               note_start_tag, the_reaction.subsystem, note_end_tag))

    if use_fbc_package:
        try:
            from libsbml import ConversionProperties, LIBSBML_OPERATION_SUCCESS
            conversion_properties = ConversionProperties()
            conversion_properties.addOption("convert cobra", True,
                                            "Convert Cobra model")
            result = sbml_doc.convert(conversion_properties)
            if result != LIBSBML_OPERATION_SUCCESS:
                raise Exception("Conversion of COBRA to SBML+fbc failed")
        except Exception as e:
            error_string = 'Error saving as SBML+fbc. %s'
            try:
                #Check whether the FbcExtension is there
                from libsbml import FbcExtension
                error_string = error_string % e
            except ImportError:
                error_string = error_string%'FbcExtension not available in libsbml. ' +\
                               'If use_fbc_package == True then libsbml must be compiled with ' +\
                               'the fbc extension. '
                from libsbml import getLibSBMLDottedVersion
                _sbml_version = getLibSBMLDottedVersion()
                _major, _minor, _patch = map(int, _sbml_version.split('.'))
                if _major < 5 or (_major == 5 and _minor < 8):
                    error_string += "You've got libsbml %s installed.   You need 5.8.0 or later with the fbc package"

            raise (Exception(error_string))
    writeSBML(sbml_doc, sbml_filename)
Example #4
0
def write_cobra_model_to_sbml_file(cobra_model, sbml_filename,
                                   sbml_level=2, sbml_version=1,
                                   print_time=False,
                                   use_fbc_package=True):
    """Write a cobra.Model object to an SBML XML file.

    cobra_model:  :class:`~cobra.core.Model.Model` object

    sbml_filename:  The file to write the SBML XML to.

    sbml_level:  2 is the only level supported at the moment.

    sbml_version: 1 is the only version supported at the moment.

    use_fbc_package: Boolean.
        Convert the model to the FBC package format to improve portability.
        http://sbml.org/Documents/Specifications/SBML_Level_3/Packages/Flux_Balance_Constraints_(flux)


    TODO: Update the NOTES to match the SBML standard and provide support for
    Level 2 Version 4

    """
    note_start_tag, note_end_tag = '<p>', '</p>'
    if sbml_level > 2 or (sbml_level == 2 and sbml_version == 4):
        note_start_tag, note_end_tag = '<html:p>', '</html:p>'
        
    
    sbml_doc = SBMLDocument(sbml_level, sbml_version)
    sbml_model = sbml_doc.createModel(cobra_model.description.split('.')[0])
    #Note need to set units
    reaction_units = 'mmol_per_gDW_per_hr'
    model_units = sbml_model.createUnitDefinition()
    model_units.setId(reaction_units)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_MOLE)
    sbml_unit.setScale(-3)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_GRAM)
    sbml_unit.setExponent(-1)
    sbml_unit = model_units.createUnit()
    sbml_unit.setKind(UNIT_KIND_SECOND)
    sbml_unit.setMultiplier(1.0/60/60)
    sbml_unit.setExponent(-1)

    #Add in the common compartment abbreviations.  If there are additional compartments
    #they also need to be added.
    if not cobra_model.compartments:
        cobra_model.compartments = {'c': 'cytosol',
                                    'p': 'periplasm',
                                    'e': 'extracellular'}    
    for the_key in cobra_model.compartments.keys():
        sbml_comp = sbml_model.createCompartment()
        sbml_comp.setId(the_key)
        sbml_comp.setName(cobra_model.compartments[the_key])
        sbml_comp.setSize(1) #Just to get rid of warnings

    if print_time:
        warn("print_time is deprecated")
    #Use this dict to allow for fast look up of species id
    #for references created in the reaction section.
    metabolite_dict = {}

    for cobra_metabolite in cobra_model.metabolites:
        metabolite_dict[cobra_metabolite.id] =  add_sbml_species(sbml_model,
                                                                 cobra_metabolite,
                                                                 note_start_tag=note_start_tag,
                                                                 note_end_tag=note_end_tag)

    for the_reaction in cobra_model.reactions:
        #This is probably the culprit.  Including cobra.Reaction
        #objects explicitly in cobra.Model will speed this up.
        sbml_reaction = sbml_model.createReaction()
        #Need to remove - for proper SBML.  Replace with __
        the_reaction_id = 'R_' + the_reaction.id.replace('-','__' )
        sbml_reaction.setId(the_reaction_id)
        sbml_reaction.setReversible(the_reaction.reversibility)
        if the_reaction.name:
            sbml_reaction.setName(the_reaction.name)
        else:
            sbml_reaction.setName(the_reaction.id)
        #Add in the reactant/product references
        for the_metabolite, the_coefficient in the_reaction._metabolites.items():
            sbml_stoichiometry = the_coefficient
            metabolite_id = str(metabolite_dict[the_metabolite.id])
            #Each SpeciesReference must have a unique id
            if sbml_stoichiometry < 0:
                species_reference = sbml_reaction.createReactant()
            else:
                species_reference = sbml_reaction.createProduct()
            species_reference.setId(metabolite_id + '_' + the_reaction_id)
            species_reference.setSpecies(metabolite_id)
            species_reference.setStoichiometry(abs(sbml_stoichiometry))
        #Deal with the case where the reaction is a boundary reaction
        if len(the_reaction._metabolites) == 1:
            the_metabolite, the_coefficient = list(the_reaction._metabolites.items())[0]
            the_metabolite = the_metabolite.copy()
            metabolite_id = add_sbml_species(sbml_model, the_metabolite,
                                             note_start_tag=note_start_tag,
                                             note_end_tag=note_end_tag,
                                             boundary_metabolite=True)
            sbml_stoichiometry = -the_coefficient
            #Each SpeciesReference must have a unique id
            if sbml_stoichiometry < 0:
                species_reference = sbml_reaction.createReactant()
            else:
                species_reference = sbml_reaction.createProduct()
            species_reference.setId(metabolite_id + '_' + the_reaction_id)
            species_reference.setSpecies(metabolite_id)
            species_reference.setStoichiometry(abs(sbml_stoichiometry))
            
        #Add in the kineticLaw
        sbml_law = KineticLaw(sbml_level, sbml_version)
        if hasattr(sbml_law, 'setId'):
            sbml_law.setId('FLUX_VALUE')
        sbml_law.setFormula('FLUX_VALUE')
        reaction_parameter_dict = {'LOWER_BOUND': [the_reaction.lower_bound, reaction_units],
                                   'UPPER_BOUND': [the_reaction.upper_bound, reaction_units],
                                   'FLUX_VALUE': [0, reaction_units],
                                   'OBJECTIVE_COEFFICIENT': [the_reaction.objective_coefficient,
                                                             'dimensionless']}
        for k, v in reaction_parameter_dict.items():
            sbml_parameter = Parameter(sbml_level, sbml_version)
            sbml_parameter.setId(k)
            if hasattr(v, '__iter__'):
                sbml_parameter.setValue(v[0])
                sbml_parameter.setUnits(v[1])
            else:
                sbml_parameter.setValue(v)
            sbml_law.addParameter(sbml_parameter)
        sbml_reaction.setKineticLaw(sbml_law)
        sbml_reaction.setNotes('<html xmlns="http://www.w3.org/1999/xhtml">%sGENE_ASSOCIATION: %s%s%sSUBSYSTEM: %s%s</html>'%(note_start_tag,
                                                                 the_reaction.gene_reaction_rule,
                                                                 note_end_tag,
                                                                 note_start_tag,
                                                                 the_reaction.subsystem,
                                                                 note_end_tag))


    if use_fbc_package:
        try:
            from libsbml import ConversionProperties, LIBSBML_OPERATION_SUCCESS
            conversion_properties = ConversionProperties()
            conversion_properties.addOption("convert cobra", True, "Convert Cobra model")
            result = sbml_doc.convert(conversion_properties)
            if result != LIBSBML_OPERATION_SUCCESS:
                raise Exception("Conversion of COBRA to SBML+fbc failed")
        except Exception as e:
            error_string = 'Error saving as SBML+fbc. %s'
            try:
                #Check whether the FbcExtension is there
                from libsbml import FbcExtension
                error_string = error_string%e
            except ImportError:
                error_string = error_string%'FbcExtension not available in libsbml. ' +\
                               'If use_fbc_package == True then libsbml must be compiled with ' +\
                               'the fbc extension. '
                from libsbml import getLibSBMLDottedVersion
                _sbml_version = getLibSBMLDottedVersion()
                _major, _minor, _patch = map(int, _sbml_version.split('.'))
                if _major < 5 or (_major == 5 and _minor < 8):
                    error_string += "You've got libsbml %s installed.   You need 5.8.0 or later with the fbc package"

            raise(Exception(error_string))
    writeSBML(sbml_doc, sbml_filename)