Bug#949287: sagemath-common: Fail to start because of missing unicode_to_str from IPython.utils.py3compat

[Amaury Pouly]

Package: sagemath-common
Version: 8.9-3
Severity: important

Dear Maintainer,

Sagemath is unusable (both in command line or through jupyter) because of an import error.
Specifically, trying to run sage or load a notebook throws the following backtrace:

Traceback (most recent call last):
  File "/usr/lib/python3.7/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/lib/python3/dist-packages/sage/repl/ipython_kernel/__main__.py", line 3, in <module>
    IPKernelApp.launch_instance(kernel_class=SageKernel)
  File "/usr/lib/python3/dist-packages/traitlets/config/application.py", line 663, in launch_instance
    app.initialize(argv)
  File "<decorator-gen-124>", line 2, in initialize
  File "/usr/lib/python3/dist-packages/traitlets/config/application.py", line 87, in catch_config_error
    return method(app, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/ipykernel/kernelapp.py", line 542, in initialize
    self.init_kernel()
  File "/usr/lib/python3/dist-packages/ipykernel/kernelapp.py", line 447, in init_kernel
    user_ns=self.user_ns,
  File "/usr/lib/python3/dist-packages/traitlets/config/configurable.py", line 412, in instance
    inst = cls(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/sage/repl/ipython_kernel/kernel.py", line 51, in __init__
    super(SageKernel, self).__init__(**kwds)
  File "/usr/lib/python3/dist-packages/ipykernel/ipkernel.py", line 68, in __init__
    kernel      = self,
  File "/usr/lib/python3/dist-packages/traitlets/config/configurable.py", line 412, in instance
    inst = cls(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/IPython/core/interactiveshell.py", line 683, in __init__
    self.init_display_formatter()
  File "/usr/lib/python3/dist-packages/sage/repl/interpreter.py", line 231, in init_display_formatter
    backend.get_display_manager().switch_backend(backend, shell=self)
  File "/usr/lib/python3/dist-packages/sage/repl/rich_output/display_manager.py", line 322, in switch_backend
    self._backend.install(**kwds)
  File "/usr/lib/python3/dist-packages/sage/repl/rich_output/backend_ipython.py", line 59, in install
    from sage.repl.display.formatter import SageDisplayFormatter
  File "/usr/lib/python3/dist-packages/sage/repl/display/formatter.py", line 64, in <module>
    from IPython.utils.py3compat import unicode_to_str
ImportError: cannot import name 'unicode_to_str' from 'IPython.utils.py3compat' (/usr/lib/python3/dist-packages/IPython/utils/py3compat.py)

-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.4.2-amdmp2 (SMP w/8 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8), LANGUAGE=fr (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages sagemath-common depends on:
ii  python3  3.7.5-3

sagemath-common recommends no packages.

sagemath-common suggests no packages.

-- no debconf information