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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def direction(theta, phi):
    '''Return the direction vector of a cylinder defined
    by the spherical coordinates theta and phi.
    '''
    return np.array([np.cos(phi) * np.sin(theta), np.sin(phi) * np.sin(theta),
                     np.cos(theta)])