[BUG] unexpected type Py_UCS4 and base type Python object for indexing

[NilsBrause]

Hi!

When trying to cythonize the following source code using cythonize -3:

str(0)[0]

the following error is printed:

Traceback (most recent call last):
  File "/home/nils/.local/bin/cythonize", line 8, in <module>
    sys.exit(main())
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Build/Cythonize.py", line 224, in main
    cython_compile(path, options)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Build/Cythonize.py", line 68, in cython_compile
    ext_modules = cythonize(
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Build/Dependencies.py", line 1117, in cythonize
    cythonize_one(*args)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Build/Dependencies.py", line 1263, in cythonize_one
    result = compile_single(pyx_file, options, full_module_name=full_module_name)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/Main.py", line 576, in compile_single
    return run_pipeline(source, options, full_module_name)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/Main.py", line 504, in run_pipeline
    err, enddata = Pipeline.run_pipeline(pipeline, source)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/Pipeline.py", line 394, in run_pipeline
    data = run(phase, data)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/Pipeline.py", line 371, in run
    return phase(data)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/Pipeline.py", line 52, in generate_pyx_code_stage
    module_node.process_implementation(options, result)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/ModuleNode.py", line 206, in process_implementation
    self.generate_c_code(env, options, result)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/ModuleNode.py", line 518, in generate_c_code
    self.generate_module_init_func(modules[:-1], env, globalstate['init_module'])
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/ModuleNode.py", line 3101, in generate_module_init_func
    self.body.generate_execution_code(code)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/Nodes.py", line 409, in generate_execution_code
    stat.generate_execution_code(code)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/Nodes.py", line 5700, in generate_execution_code
    self.expr.generate_evaluation_code(code)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/ExprNodes.py", line 834, in generate_evaluation_code
    self.generate_result_code(code)
  File "/home/nils/.local/lib/python3.10/site-packages/Cython/Compiler/ExprNodes.py", line 4213, in generate_result_code
    assert False, "unexpected type %s and base type %s for indexing" % (
AssertionError: unexpected type Py_UCS4 and base type Python object for indexing

To my understanding, str(0)[0] should evaluate to '0', which is the first character of the string representation of 0.
Surprisingly, I don't get any error using cythonize --3str or cythonize -2. It also works to first assign the result of str(0) to a variable:

a = str(0)
a[0]

Environment:

• OpenSUSE Leap 15.3
• Python 3.10
• Cython 3.0.0a10

[matthewdeanmartin]

I got the same for Cython==3.0.8, windows 11, python 3.11.1.

I switched to --3str and now I get different errors on fstrings

return f"{self.prefix}-{value}"
               ^
helpers\requests.py:58:15: Cannot convert Unicode string to 'str' implicitly. This is not portable and requires explicit encoding.

[scoder]

Thanks for the reports, I could reproduce the original issue on the latest master. It's easy to fix there, because it's limited to Python 3.x. A backport to Cython 3.0 might be less easy.

[scoder]

I switched to --3str and now I get different errors on fstrings

return f"{self.prefix}-{value}"
               ^
helpers\requests.py:58:15: Cannot convert Unicode string to 'str' implicitly. This is not portable and requires explicit encoding.

You probably declared your return type as str. However, f-strings always return unicode strings, not str (which is bytes in Py2). Declare the return type as unicode instead.

[numbworks]

Thank you @scoder for your hint! It solved the issue for me!

I used to get the same error message on the following method:

  def create_numbered_file_path(self, folder_path : str, number : int, extension : str) -> str:

      r'''Creates a numbered file path. Example: ("C:\\", 1, "html") => "C:\\1.html"'''

      file_name : str = f"{number}.{extension}"
      file_path : str = self.create_file_path(folder_path = folder_path, file_name = file_name)    

      return file_path

Using str() around the f-string solved the issue:

      # ...
      file_name : str = str(f"{number}.{extension}")
      # ...      

Information:

• Windows 10
• Python 3.12.1
• cython-3.0.10
• setuptools-69.2.0
• Command: python demolibrary1_setup.py build_ext --inplace
• Error Message (truncated):

...
    def create_numbered_file_path(self, folder_path : str, number : int, extension : str) -> str:

        r'''Creates a numbered file path. Example: ("C:\\", 1, "html") => "C:\\1.html"'''

        file_name : str = f"{number}.{extension}"
                          ^
------------------------------------------------------------

demolibrary1.py:18:26: Cannot convert Unicode string to 'str' implicitly. This is not portable and requires explicit encoding.
...