code: def Tz(self,**kwargs): #pragma: no cover
          
          if hasattr(self,'_Tz'):
              return self._Tz
          zmax= self.calczmax()
          Ez= calcEz(self._z,self._vz,self._verticalpot)
          self._Tz= 4.*integrate.quad(_TzIntegrand,0.,zmax,
                                      args=(Ez,self._verticalpot),
                                      **kwargs)[0]
          return self._Tz
docs: NAME:
             Tz
          PURPOSE:
             Calculate the vertical period
          INPUT:
             +scipy.integrate.quad keywords
          OUTPUT:
             T_z(z,vz)*vc/ro + estimate of the error
          HISTORY:
             2012-06-01 - Written - Bovy (IAS)