13. FAQ

This document will address frequently asked questions not addressed in other pages of the documentation.

13.1. How do I install cobrapy?

Please see the INSTALL.rst file.

13.2. How do I cite cobrapy?

Please cite the 2013 publication: 10.1186/1752-0509-7-74

13.3. How do I rename reactions or metabolites?

TL;DR Use Model.repair afterwards

When renaming metabolites or reactions, there are issues because cobra indexes based off of ID’s, which can cause errors. For example:

In [1]:
from __future__ import print_function
import cobra.test
model = cobra.test.create_test_model()

for metabolite in model.metabolites:
    metabolite.id = "test_" + metabolite.id

except KeyError as e:
/home/moritz/.virtualenvs/cobra/lib/python3.5/site-packages/optlang/gurobi_interface.py:26: UserWarning: Be careful! The GUROBI interface is still under construction ...
  warn("Be careful! The GUROBI interface is still under construction ...")

The Model.repair function will rebuild the necessary indexes

In [2]:
<Metabolite test_dcaACP_c at 0x7fa92b9257f0>

13.4. How do I delete a gene?

That depends on what precisely you mean by delete a gene.

If you want to simulate the model with a gene knockout, use the cobra.manipulation.delete_model_genes function. The effects of this function are reversed by cobra.manipulation.undelete_model_genes.

In [3]:
model = cobra.test.create_test_model()
PGI = model.reactions.get_by_id("PGI")
print("bounds before knockout:", (PGI.lower_bound, PGI.upper_bound))
cobra.manipulation.delete_model_genes(model, ["STM4221"])
print("bounds after knockouts", (PGI.lower_bound, PGI.upper_bound))
bounds before knockout: (-1000.0, 1000.0)
bounds after knockouts (0.0, 0.0)

If you want to actually remove all traces of a gene from a model, this is more difficult because this will require changing all the gene_reaction_rule strings for reactions involving the gene.

13.5. How do I change the reversibility of a Reaction?

Reaction.reversibility is a property in cobra which is computed when it is requested from the lower and upper bounds.

In [4]:
model = cobra.test.create_test_model()

Trying to set it directly will result in an error or warning:

In [5]:
    model.reactions.get_by_id("PGI").reversibility = False
except Exception as e:
cobra/core/reaction.py:484 UserWarning: Setting reaction reversibility is ignored

The way to change the reversibility is to change the bounds to make the reaction irreversible.

In [6]:
model.reactions.get_by_id("PGI").lower_bound = 10

13.6. How do I generate an LP file from a COBRA model?

13.6.1. For optlang based solvers

With optlang solvers, the LP formulation of a model is obtained by it’s string representation. All solvers behave the same way.

In [7]:
with open('test.lp', 'w') as out:

13.6.2. For cobrapy’s internal solvers

With the internal solvers, we first create the problem and use functions bundled with the solver.

Please note that unlike the LP file format, the MPS file format does not specify objective direction and is always a minimization. Some (but not all) solvers will rewrite the maximization as a minimization.

In [8]:
model = cobra.test.create_test_model()
# glpk through cglpk
glpk = cobra.solvers.cglpk.create_problem(model)
glpk.write("test.mps")  # will not rewrite objective
# cplex
cplex = cobra.solvers.cplex_solver.create_problem(model)
cplex.write("test.mps")  # rewrites objective

13.6.3. How do I visualize my flux solutions?

cobrapy works well with the escher package, which is well suited to this purpose. Consult the escher documentation for examples.