How can I use external types in Cython class?

I am converting a vanilla python to cython to speed up the performance. I need to define a class PFR with an attribute gas. The type of gas is Solution which is a type from an external library called cantera (written in C++ with a python interface created using Cython).

# distutils: language=c++
cimport cantera as ct

cdef class PFR:
    cdef public ct.Solution gas;
    def __init__(self):
        self.gas = None;

    def set_gas(self, gas):
        self.gas = gas

When I complie the code I get this error:

    Error compiling Cython file:
------------------------------------------------------------
...
# distutils: language=c++
cimport cantera as ct

cdef class PFR:
    cdef public ct.Solution gas;
               ^
------------------------------------------------------------

C:\Users\[****]\.ipython\cython\_cython_magic_d7002e8c4a676e8ba0827e69fe89ba2a.pyx:5:16: 'Solution' is not a type identifier

Error compiling Cython file:
------------------------------------------------------------
...
# distutils: language=c++
cimport cantera as ct

cdef class PFR:
    cdef public ct.Solution gas;
                           ^
------------------------------------------------------------

C:\Users\[****]\.ipython\cython\_cython_magic_d7002e8c4a676e8ba0827e69fe89ba2a.pyx:5:28: C attribute of type '<error>' cannot be accessed from Python

I found a trick to make the code work. I declare gas initially as a object instead of ct.Solution

# distutils: language=c++
import cantera as ct

cdef class PFR:
    cdef public object gas;
    def __init__(self):
        self.gas = None;

    def set_gas(self, gas):
        self.gas = gas;

    def set_TP(self, T, P):
        self.gas.TP = T, P

This works fine without any errors. I can create a gas object, connect it to an instance of PFR using the gas attribute and modify it using set.TP(T,P) method.

But, I am not sure if this approach is correct because I do not understand what is happening under the hood. Could this cause performance errors when I expand the class or create multiple instances of PFR?