Unicode Error when launching PSI4 driver (using Windows)

When using psi4 as driver for my vqe calculations, I get the following error:

Traceback (most recent call last):
  File "C:\Users\poc\Anaconda3\envs\qiskit-0-27-psi4-jupyter\Scripts\psi4-script.py", line 336, in <module>
    exec(content)

  File "<string>", line 31
SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 2-3: truncated \UXXXXXXXX escape

Printing out the relevant lines from the Psithon --> Python processed input file:


!----------------------------------------------------------------------------------!
!                                                                                  !
!  (unicode error) 'unicodeescape' codec can't decode bytes in position 2-3:       !
!     truncated \UXXXXXXXX escape                                                  !
!                                                                                  !
!----------------------------------------------------------------------------------!

Traceback (most recent call last):
  File "c:\Users\poc\Documents\qiskit_scripts\groundstatesolver.py", line 336, in <module>
    compare_mappers()
  File "c:\Users\poc\Documents\qiskit_scripts\groundstatesolver.py", line 206, in compare_mappers
    second_q_op = es_problem.second_q_ops()
  File "C:\Users\poc\Anaconda3\envs\qiskit-0-27-psi4-jupyter\lib\site-packages\qiskit_nature\problems\second_quantization\electronic\electronic_structure_problem.py", line 64, in second_q_ops
    self._molecule_data = cast(QMolecule, self.driver.run())
  File "C:\Users\poc\Anaconda3\envs\qiskit-0-27-psi4-jupyter\lib\site-packages\qiskit_nature\drivers\psi4d\psi4driver.py", line 160, in run
    PSI4Driver._run_psi4(input_file, output_file)
  File "C:\Users\poc\Anaconda3\envs\qiskit-0-27-psi4-jupyter\lib\site-packages\qiskit_nature\drivers\psi4d\psi4driver.py", line 215, in _run_psi4
    raise QiskitNatureError('{} process return code {}\n{}'.format(
qiskit_nature.exceptions.QiskitNatureError: 'psi4 process return code 1\nTraceback (most recent call last):\n  File "C:\\Users\\poc\\Anaconda3\\envs\\qiskit-0-27-psi4-jupyter\\Scripts\\psi4-script.py", line 336, in <module>\n    exec(content)\n\n  File "<string>", line 31\nSyntaxError: (unicode error) \'unicodeescape\' codec can\'t decode bytes in position 2-3: truncated \\UXXXXXXXX escape\n\nPrinting out the relevant lines from the Psithon --> Python processed input file:\n\n\n!----------------------------------------------------------------------------------!\n!                                                                                  !\n!  (unicode error) \'unicodeescape\' codec can\'t decode bytes in position 2-3:       !\n!     truncated \\UXXXXXXXX escape                                                  !\n!                                                                                  !\n!----------------------------------------------------------------------------------!\n\n'

With the kind help of some psi4 developers I could track down it to these lines: https://github.com/Qiskit/qiskit-nature/blob/c7fa055cfba2dc08daef0111e569ae5eb9bce10b/qiskit_nature/drivers/psi4d/psi4driver.py#L123-L133

I was able to get rid of the problem via changing above lines to this:

        qiskit_nature_directory = os.path.abspath(os.path.join(psi4d_directory, "../.."))

        molecule = QMolecule()

        input_text = cfg + "\n"
        input_text += "import sys\n"
        syspath = "['" + qiskit_nature_directory.replace("\\", "\\\\") + "','" + "','".join(p.replace("\\", "\\\\") for p in sys.path) + "']"

        input_text += "sys.path = " + syspath + " + sys.path\n"
        input_text += "from qiskit_nature.drivers.qmolecule import QMolecule\n"
        input_text += "_q_molecule = QMolecule('" + molecule.filename.replace("\\", "\\\\") + "')\n"

Unfortunately this fix is not cross-platform compatible but quite windows-specific. So, any help finding a nice fix for this bug or even a simplified/less error-prone way to call psi4 would be appreciated.

[woodsp-ibm]

We should leave this open until the PR that fixes this #262 is merged. I edited it so once it merges it will auto-close this.

[mrossinek]

If the problem of this issue is related to paths I suggest looking into pathlib to replace the os.path usage. It has built-in platform support/detection and should simplify these things a lot.