Frequently Asked Questions

Or more likely Frequent Error Debugging.

Encoding Errors: UnicodeDecodeError

If you received the error below while opening a file in MontePy, there is like a non-ASCII character in your input file. You can read more about Character Encoding here.

To solve this problem you can:

1. Try another encoding such as 'utf8' or 'cp1252'. Pass it as an argument to read_input().

2. Remove all non-ASCII characters with the change_to_ascii utility

---------------------------------------------------------------------------
  UnicodeDecodeError                        Traceback (most recent call last)
  Cell In[2], line 1
  ----> 1 problem = montepy.read_input("tests/inputs/bad_encoding.imcnp")

  File ~/dev/montepy/montepy/input_parser/input_reader.py:35, in read_input(input_file, mcnp_version, encoding)
       33 problem = mcnp_problem.MCNP_Problem(input_file)
       34 problem.mcnp_version = mcnp_version
  ---> 35 problem.parse_input(encoding=encoding)
       36 return problem

  File ~/dev/montepy/montepy/mcnp_problem.py:262, in MCNP_Problem.parse_input(self, check_input, encoding)
      253 OBJ_MATCHER = {
      254     block_type.BlockType.CELL: (Cell, self._cells),
      255     block_type.BlockType.SURFACE: (
     (...)
      259     block_type.BlockType.DATA: (parse_data, self._data_inputs),
      260 }
      261 try:
  --> 262     for i, input in enumerate(
      263         input_syntax_reader.read_input_syntax(
      264             self._input_file, self.mcnp_version, encoding=encoding
      265         )
      266     ):
      267         self._original_inputs.append(input)
      268         if i == 0 and isinstance(input, mcnp_input.Message):

  File ~/dev/montepy/montepy/input_parser/input_syntax_reader.py:48, in read_input_syntax(input_file, mcnp_version, encoding)
       46 reading_queue = deque()
       47 with input_file.open("r", encoding=encoding) as fh:
  ---> 48     yield from read_front_matters(fh, mcnp_version)
       49     yield from read_data(fh, mcnp_version)

  File ~/dev/montepy/montepy/input_parser/input_syntax_reader.py:79, in read_front_matters(fh, mcnp_version)
       77 lines = []
       78 raw_lines = []
  ---> 79 for i, line in enumerate(fh):
       80     if i == 0 and line.upper().startswith("MESSAGE:"):
       81         is_in_message_block = True

  File ~/dev/montepy/montepy/input_parser/input_file.py:95, in MCNP_InputFile.__iter__(self)
       94 def __iter__(self):
  ---> 95     for lineno, line in enumerate(self._fh):
       96         self._lineno = lineno + 1
       97         yield line

  File ~/mambaforge/lib/python3.10/encodings/ascii.py:26, in IncrementalDecoder.decode(self, input, final)
       25 def decode(self, input, final=False):
  ---> 26     return codecs.ascii_decode(input, self.errors)[0]

  UnicodeDecodeError: 'ascii' codec can't decode byte 0xff in position 159: ordinal not in range(128)

Will MCNP Output Files Ever be Supported?

Short answer: no.

For a longer answer see this discussion in the scope of MontePy: Support of MCNP Output Files.