In [14]: %run piston.py
time [s]    T1 [K]      T2 [K]      V1 [m^3]    V2 [m^3]    V1+V2 [m^3]  X(CO)     
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/src/interfaces/cython/cantera/examples/reactors/piston.py in <module>()
     54 net = ct.ReactorNet([r1, r2])
     55 
---> 56 states1 = ct.SolutionArray(r1.thermo, extra=['t', 'v'])
     57 states2 = ct.SolutionArray(r2.thermo, extra=['t', 'v'])
     58 

/usr/local/lib/python3.6/dist-packages/cantera/composite.py in __init__(self, phase, shape, states, extra, meta)
    548                     raise ValueError(
    549                         "Unable to create extra column '{}': name is already "
--> 550                         "used by SolutionArray objects.".format(name))
    551                 self._extra[name] = []
    552 

ValueError: Unable to create extra column 'v': name is already used by SolutionArray objects.