AssertionError hiding my mistake

I accidentally returned an internal type instead of a str from my custom completer and got this exception:

Traceback (most recent call last):
  File "doc_prompt_toolkit.py", line 25, in <module>
    text = prompt('Column', completer=completer, bottom_toolbar='. to see shortcuts, ( to see constructor arguments')
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 803, in prompt
    return session.prompt(*a, **kw)
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 731, in prompt
    return run_sync()
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 715, in run_sync
    return self.app.run(inputhook=self.inputhook, pre_run=pre_run)
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/application/application.py", line 682, in run
    return run()
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/application/application.py", line 656, in run
    return f.result()
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/eventloop/future.py", line 149, in result
    raise self._exception
AssertionError

The original assertion error stack trace is lost. So I fiddled with the code and made it not catch this exception and store it and then I got:

Traceback (most recent call last):
  File "doc_prompt_toolkit.py", line 27, in <module>
    text = prompt('Column', completer=completer, bottom_toolbar='. to see shortcuts, ( to see constructor arguments')
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 803, in prompt
    return session.prompt(*a, **kw)
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 731, in prompt
    return run_sync()
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 715, in run_sync
    return self.app.run(inputhook=self.inputhook, pre_run=pre_run)
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/application/application.py", line 682, in run
    return run()
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/application/application.py", line 654, in run
    f = self.run_async(pre_run=pre_run)
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/application/application.py", line 640, in run_async
    return ensure_future(_run_async2())
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/eventloop/coroutine.py", line 21, in ensure_future
    return _run_coroutine(future_or_coroutine)
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/eventloop/coroutine.py", line 115, in _run_coroutine
    step_next()
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/eventloop/coroutine.py", line 104, in step_next
    ref.future.set_exception(e)
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/eventloop/coroutine.py", line 86, in step_next
    new_f = coroutine.send(None)
  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/application/application.py", line 637, in _run_async2
    assert not self._is_running
AssertionError

This isn’t very helpful either, the original exception is still gone! So I commented out this assertion and then I got the real error:

  File "/Users/andersh/Projects/tri.table/venv/lib/python2.7/site-packages/prompt_toolkit/formatted_text/base.py", line 50, in to_formatted_text
    'HTML, ANSI or a FormattedText instance. Got %r' % value)
ValueError: No formatted text. Expecting a unicode object, HTML, ANSI or a FormattedText instance. Got 'Column'

That error message is very helpful but it was very hard to get to it. It would have been better to print that exception and stack trace and directly doing exit(1) for example.

[jonathanslenders]

Hi @boxed,

In Python 3, all the exceptions are chained and will be printed. For Python 2, you can disable the assertions by passing the -O option to the Python interpreter.

I think that the object that you have there is a str in Python 2 instead of a unicode object. Maybe try to use either from __future__ import unicode_literals, or prefix 'Column' with a u : u'Column'.

[jonathanslenders]

Closing this. Feel free to open again if needed.