IndexError in start_ipython when sys.argv is empty

[mroethke]

When sys.argv is empty and start_ipython is called the following exception occurs:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.7/site-packages/IPython/__init__.py", line 125, in start_ipython
    return launch_new_instance(argv=argv, **kwargs)
  File "/usr/lib/python3.7/site-packages/traitlets/config/application.py", line 663, in launch_instance
    app.initialize(argv)
  File "</usr/lib/python3.7/site-packages/decorator.py:decorator-gen-113>", line 2, in initialize
  File "/usr/lib/python3.7/site-packages/traitlets/config/application.py", line 87, in catch_config_error
    return method(app, *args, **kwargs)
  File "/usr/lib/python3.7/site-packages/IPython/terminal/ipapp.py", line 308, in initialize
    super(TerminalIPythonApp, self).initialize(argv)
  File "</usr/lib/python3.7/site-packages/decorator.py:decorator-gen-7>", line 2, in initialize
  File "/usr/lib/python3.7/site-packages/traitlets/config/application.py", line 87, in catch_config_error
    return method(app, *args, **kwargs)
  File "/usr/lib/python3.7/site-packages/IPython/core/application.py", line 450, in initialize
    self.parse_command_line(argv)
  File "/usr/lib/python3.7/site-packages/IPython/terminal/ipapp.py", line 303, in parse_command_line
    return super(TerminalIPythonApp, self).parse_command_line(argv)
  File "</usr/lib/python3.7/site-packages/decorator.py:decorator-gen-4>", line 2, in parse_command_line
  File "/usr/lib/python3.7/site-packages/traitlets/config/application.py", line 87, in catch_config_error
    return method(app, *args, **kwargs)
  File "/usr/lib/python3.7/site-packages/traitlets/config/application.py", line 538, in parse_command_line
    self.cli_config = deepcopy(loader.load_config())
  File "/usr/lib/python3.7/site-packages/traitlets/config/loader.py", line 745, in load_config
    self._create_parser(aliases, flags)
  File "/usr/lib/python3.7/site-packages/traitlets/config/loader.py", line 757, in _create_parser
    self.parser = ArgumentParser(*self.parser_args, **self.parser_kw)
  File "/usr/lib/python3.7/argparse.py", line 1641, in __init__
    prog = _os.path.basename(_sys.argv[0])
IndexError: list index out of range

This can be reproduced with this slightly contrived example:

import sys
import IPython
sys.argv = [] 
IPython.start_ipython(argv=[])

As shown in the example it even happens when the argument argv is an empty list, even though the documentation says this disables argument parsing entirely.

System Info:

{'commit_hash': '<not found>',
 'commit_source': '(none found)',
 'default_encoding': 'UTF-8',
 'ipython_path': '/usr/lib/python3.7/site-packages/IPython',
 'ipython_version': '7.8.0',
 'os_name': 'posix',
 'platform': 'Linux-5.3.6-arch1-1-ARCH-x86_64-with-arch',
 'sys_executable': '/usr/bin/python',
 'sys_platform': 'linux',
 'sys_version': '3.7.4 (default, Oct  4 2019, 06:57:26) \n[GCC 9.2.0]'}

However I can reproduce this with IPython versions as old as 4.2.1

[Carreau]

Hum, it's contrived but I believe this is an actual bug, though it will be in tartlets; not in IPython itself.

[mroethke]

The example I provided is contrived yes, but that just the result of condensing it to its minimal form.
I did actually encountered this in in an environment where python was embedded with ipython as an interactive shell for some native functions. sys.argv is empty in that environment.

[MrMino]

Still reproducible on IPython 8.1.1 / traitlets 5.1.1.