There are a total of 119 metabolites (8.91%) without a formula: __iYS854__12napdol_c, __iYS854__2mehbtpp_c, __iYS854__12diisgly_c, __iYS854__33hmeoxobut_c, __iYS854__3c1ht_c, ...

To be able to ensure that reactions are mass-balanced, all model metabolites ought to be provided with a chemical formula. Since it may be difficult to obtain formulas for certain metabolites this test serves as a mere report. Models can still be stoichiometrically consistent even when chemical formulas are not defined for each metabolite. Implementation: Check if each cobra.Metabolite has a non-empty "formula" attribute. This attribute is set by the parser if there is an fbc:chemicalFormula attribute for the corresponding species in the SBML.