I have a C++ function returning a std::vector and I want to use it in python, so I'm using the C numpy api:

static PyObject *
py_integrate(PyObject *self, PyObject *args){
...
std::vector<double> integral;
cpp_function(integral);    // this change integral
npy_intp size = {integral.size()};
PyObject *out = PyArray_SimpleNewFromData(1, &size, NPY_DOUBLE, &(integral[0]));
return out;
}

when I call it from python, if I do

import matplotlib.pyplot as plt

a = py_integrate(parameters)
print a
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(a)
print a

the first print is ok, the values are correct, but when I plot a they are not, and in particular in the second print I see very strange values like 1E-308 1E-308 ... or 0 0 0 ... as an unitialized memory. I don't understand why the first print is ok.