# This file is part of QuTiP: Quantum Toolbox in Python.
#
#    Copyright (c) 2011 and later, Paul D. Nation.
#    All rights reserved.
#
#    Redistribution and use in source and binary forms, with or without
#    modification, are permitted provided that the following conditions are
#    met:
#
#    1. Redistributions of source code must retain the above copyright notice,
#       this list of conditions and the following disclaimer.
#
#    2. Redistributions in binary form must reproduce the above copyright
#       notice, this list of conditions and the following disclaimer in the
#       documentation and/or other materials provided with the distribution.
#
#    3. Neither the name of the QuTiP: Quantum Toolbox in Python nor the names
#       of its contributors may be used to endorse or promote products derived
#       from this software without specific prior written permission.
#
#    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
#    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
#    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
#    PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
#    HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
#    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
#    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
#    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
#    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
#    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
#    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
###############################################################################
import numpy as np
import scipy.sparse as sp
import ctypes
from ctypes import POINTER,c_int,c_char,c_double, byref
from numpy import ctypeslib
import qutip.settings as qset
zcsrgemv = qset.mkl_lib.mkl_cspblas_zcsrgemv

def mkl_spmv(A, x):
     """
     sparse csr_spmv using MKL
     """
     (m,n) = A.shape

     # Pointers to data of the matrix
     data    = A.data.ctypes.data_as(ctypeslib.ndpointer(np.complex128, ndim=1, flags='C'))
     indptr  = A.indptr.ctypes.data_as(POINTER(c_int))
     indices = A.indices.ctypes.data_as(POINTER(c_int))

     # Allocate output, using same conventions as input
     if x.ndim is 1:
        y = np.empty(m,dtype=np.complex,order='C')
     elif x.ndim==2 and x.shape[1]==1:
        y = np.empty((m,1),dtype=np.complex,order='C')
     else:
        raise Exception('Input vector must be 1D row or 2D column vector')
     
     np_x = x.ctypes.data_as(ctypeslib.ndpointer(np.complex128, ndim=1, flags='C'))
     np_y = y.ctypes.data_as(ctypeslib.ndpointer(np.complex128, ndim=1, flags='C'))
     # now call MKL. This returns the answer in np_y, which points to y
     zcsrgemv(byref(c_char(bytes(b'N'))), byref(c_int(m)), data ,indptr, indices, np_x, np_y ) 
     return y

qutip/_mkl/spmv.py
# This file is part of QuTiP: Quantum Toolbox in Python.
#
#    Copyright (c) 2011 and later, Paul D. Nation.
#    All rights reserved.
#
#    Redistribution and use in source and binary forms, with or without
#    modification, are permitted provided that the following conditions are
#    met:
#
#    1. Redistributions of source code must retain the above copyright notice,
#       this list of conditions and the following disclaimer.
#
#    2. Redistributions in binary form must reproduce the above copyright
#       notice, this list of conditions and the following disclaimer in the
#       documentation and/or other materials provided with the distribution.
#
#    3. Neither the name of the QuTiP: Quantum Toolbox in Python nor the names
#       of its contributors may be used to endorse or promote products derived
#       from this software without specific prior written permission.
#
#    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
#    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
#    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
#    PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
#    HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
#    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
#    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
#    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
#    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
#    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
#    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
###############################################################################
import numpy as np
import scipy.sparse as sp
import ctypes
from ctypes import POINTER,c_int,c_char,c_double, byref
from numpy import ctypeslib
import qutip.settings as qset
zcsrgemv = qset.mkl_lib.mkl_cspblas_zcsrgemv

def mkl_spmv(A, x):
     """
     sparse csr_spmv using MKL
     """
     (m,n) = A.shape

     # Pointers to data of the matrix
     data    = A.data.ctypes.data_as(ctypeslib.ndpointer(np.complex128, ndim=1, flags='C'))
     indptr  = A.indptr.ctypes.data_as(POINTER(c_int))
     indices = A.indices.ctypes.data_as(POINTER(c_int))

     # Allocate output, using same conventions as input
     if x.ndim == 1:
        y = np.empty(m,dtype=np.complex,order='C')
     elif x.ndim==2 and x.shape[1]==1:
        y = np.empty((m,1),dtype=np.complex,order='C')
     else:
        raise Exception('Input vector must be 1D row or 2D column vector')
     
     np_x = x.ctypes.data_as(ctypeslib.ndpointer(np.complex128, ndim=1, flags='C'))
     np_y = y.ctypes.data_as(ctypeslib.ndpointer(np.complex128, ndim=1, flags='C'))
     # now call MKL. This returns the answer in np_y, which points to y
     zcsrgemv(byref(c_char(bytes(b'N'))), byref(c_int(m)), data ,indptr, indices, np_x, np_y ) 
     return y

qutip/_mkl/spmv.py
diff --git a/qutip/_mkl/spmv.py b/qutip/_mkl/spmv.py
index 66e9a188b3..5774ba6a64 100644
--- a/qutip/_mkl/spmv.py
+++ b/qutip/_mkl/spmv.py
@@ -50,7 +50,7 @@ def mkl_spmv(A, x):
      indices = A.indices.ctypes.data_as(POINTER(c_int))
 
      # Allocate output, using same conventions as input
-     if x.ndim is 1:
+     if x.ndim == 1:
         y = np.empty(m,dtype=np.complex,order='C')
      elif x.ndim==2 and x.shape[1]==1:
         y = np.empty((m,1),dtype=np.complex,order='C')

Installation of qutip shows various warnings on ubuntu 20.04.1
**Describe the bug**
Installing the qutip on ubuntu 20.04.1 shows the following warnings:
```
$ sudo apt install python3-qutip 
…
Entpacken von python3-qutip (4.4.1-6build1) ...
python3-qutip (4.4.1-6build1) wird eingerichtet ...
/usr/lib/python3/dist-packages/qutip/_mkl/spmv.py:53: SyntaxWarning: "is" 
with a literal. Did you mean "=="?
  if x.ndim is 1:
/usr/lib/python3/dist-packages/qutip/qobjevo.py:776: SyntaxWarning: "is no
t" with a literal. Did you mean "!="?
  if self.compiled and self.compiled.split()[2] is not "cte":
/usr/lib/python3/dist-packages/qutip/qobjevo.py:1045: SyntaxWarning: "is" 
with a literal. Did you mean "=="?
  elif op1.type is "array":
/usr/lib/python3/dist-packages/qutip/qobjevo.py:1070: SyntaxWarning: "is" 
with a literal. Did you mean "=="?
  elif self.ops[_set[0]].type is "string":
/usr/lib/python3/dist-packages/qutip/qobjevo.py:1079: SyntaxWarning: "is" 
with a literal. Did you mean "=="?
  elif self.ops[_set[0]].type is "array":
/usr/lib/python3/dist-packages/qutip/qobjevo.py:1534: SyntaxWarning: "is n
ot" with a literal. Did you mean "!="?
  for key in self.__dict__ if key is not "compiled_qobjevo"}
```


**To Reproduce**
Install qutip on ubuntu 20.04.1 via `sudo apt install python3-qutip`.

**Expected behavior**
No warnings during the installation of qutip.

**Your Environment**
```
>>> qutip.about()

QuTiP: Quantum Toolbox in Python
================================
Copyright (c) QuTiP team 2011 and later.
Original developers: R. J. Johansson & P. D. Nation.
Current admin team: Alexander Pitchford, Paul D. Nation, Nathan Shammah, Shahnawaz Ahmed, Neill Lambert, and Eric Giguère.
Project Manager: Franco Nori.
Currently developed through wide collaboration. See https://github.com/qutip for details.

QuTiP Version:      4.4.1
Numpy Version:      1.17.4
Scipy Version:      1.4.1
Cython Version:     0.29.14
Matplotlib Version: 3.1.2
Python Version:     3.8.5
Number of CPUs:     2
BLAS Info:          OPENBLAS
OPENMP Installed:   True
INTEL MKL Ext:      False
Platform Info:      Linux (x86_64)
Installation path:  /usr/lib/python3/dist-packages/qutip
```
