observe should raise with better error if wrong argument passed.

[Carreau]

Do you see the mistake :

    readline_parse_and_bind = List(default_value=[
            'tab: complete',
            '"\C-l": clear-screen',
            'set show-all-if-ambiguous on',
            '"\C-o": tab-insert',
            '"\C-r": reverse-search-history',
            '"\C-s": forward-search-history',
            '"\C-p": history-search-backward',
            '"\C-n": history-search-forward',
            '"\e[A": history-search-backward',
            '"\e[B": history-search-forward',
            '"\C-k": kill-line',
            '"\C-u": unix-line-discard',
        ]).tag(config=True)

    _custom_readline_config = False

    @observe(readline_parse_and_bind)
    def _readline_parse_and_bind_changed(self, change):
        # notice that readline config is customized
        # indicates that it should have higher priority than inputrc
        self._custom_readline_config = True

it took me 1/2 an hour to figure out I was missing a quote, because it took me 1/2 an hour to figure out which observe was wrong:

Traceback (most recent call last):
  File "/Users/bussonniermatthias/anaconda/bin/ipython", line 9, in <module>
    load_entry_point('ipython', 'console_scripts', 'ipython')()
  File "/Users/bussonniermatthias/dev/ipython/IPython/__init__.py", line 119, in start_ipython
    return launch_new_instance(argv=argv, **kwargs)
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/config/application.py", line 595, in launch_instance
    app.initialize(argv)
  File "<decorator-gen-111>", line 2, in initialize
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/config/application.py", line 74, in catch_config_error
    return method(app, *args, **kwargs)
  File "/Users/bussonniermatthias/dev/ipython/IPython/terminal/ipapp.py", line 305, in initialize
    self.init_shell()
  File "/Users/bussonniermatthias/dev/ipython/IPython/terminal/ipapp.py", line 321, in init_shell
    ipython_dir=self.ipython_dir, user_ns=self.user_ns)
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/config/configurable.py", line 405, in instance
    inst = cls(*args, **kwargs)
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/traitlets.py", line 912, in __new__
    inst.setup_instance(*args, **kwargs)
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/traitlets.py", line 940, in setup_instance
    super(HasTraits, self).setup_instance(*args, **kwargs)
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/traitlets.py", line 931, in setup_instance
    value.instance_init(self)
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/traitlets.py", line 878, in instance_init
    inst.observe(self, self.trait_names, type=self.type)
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/traitlets.py", line 1216, in observe
    names = parse_notifier_name(names)
  File "/Users/bussonniermatthias/anaconda/lib/python3.5/site-packages/traitlets/traitlets.py", line 179, in parse_notifier_name
    raise ValueError("names must be strings")
ValueError: names must be strings

If you suspect this is an IPython bug, please report it at:
    https://github.com/ipython/ipython/issues
or send an email to the mailing list at ipython-dev@scipy.org

You can print a more detailed traceback right now with "%tb", or use "%debug"
to interactively debug it.

Extra-detailed tracebacks for bug-reporting purposes can be enabled via:
    c.Application.verbose_crash=True

Could we add the name of the trait to the error message at least ?

Note that the file of the error does not even appear in the stack.

[SylvainCorlay]

👍