[bug Python3.9] "AttributeError: 'LazyChainMap' object has no attribute 'get'" when entering pdb++ breakpoint.

[jasonwirth]

Small description Entering a breakpoint (space breakpoint) throws AttributeError: 'LazyChainMap' object has no attribute 'get'.

Expected result Enter the debugger / pdb.

Actual result with screenshot

error_LazyChainMap_has_no_attribute_get.txt

Traceback (most recent call last):
  File "/Users/jasonwirth/code/visidata/visidata/basesheet.py", line 170, in execCommand
    escaped = super().execCommand2(cmd, vdglobals=vdglobals)
  File "/Users/jasonwirth/code/visidata/visidata/basesheet.py", line 72, in execCommand2
    exec(code, vdglobals, LazyChainMap(vd, self))
  File "breakpoint", line 1, in <module>
  File "/Users/jasonwirth/code/visidata/visidata/editor.py", line 88, in _breakpoint
    VisiDataPdb(nosigint=True).set_trace()
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/bdb.py", line 92, in trace_dispatch
    return self.dispatch_return(frame, arg)
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/bdb.py", line 151, in dispatch_return
    self.user_return(frame, arg)
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/pdb.py", line 294, in user_return
    self.interaction(frame, None)
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/site-packages/pdb.py", line 216, in interaction
    ret = self.setup(frame, traceback)
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/site-packages/pdb.py", line 259, in setup
    ret = super(Pdb, self).setup(frame, tb)
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/pdb.py", line 209, in setup
    self.stack, self.curindex = self.get_stack(f, tb)
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/site-packages/pdb.py", line 290, in get_stack
    return self.compute_stack(fullstack, idx)
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/site-packages/pdb.py", line 301, in compute_stack
    if self._is_hidden(frame):
  File "/Users/jasonwirth/miniconda3/envs/visidata/lib/python3.9/site-packages/pdb.py", line 282, in _is_hidden
    if frame.f_locals.get('__tracebackhide__') \
AttributeError: 'LazyChainMap' object has no attribute 'get'

Steps to reproduce with sample data and a . enter-breakpoint.vd.txt vd

sheet	col	row	longname	input	keystrokes	comment
			open-file	sample_data/countries	o	
countries		0	breakpoint			drop into pdb

Additional context

saul.pw/VisiData v2.9dev

[jasonwirth]

The fix seems somewhat trivial, add LazyChainMap.get method.

    def get(self, key, default=None, /):
        return self.objs.get(key, default=default)

However the object also maintains a locals dictionary. I'm not sure if there is a particular order, e.g. check objs first then check locals?

    def get(self, key, default=None, /):
        if key in self.objs:
            return self.objs[key]
        return self.locals.get(key, default=default)

[anjakefala]

@jasonwirth, I actually cannot reproduce this on the develop branch. Are you able to enter the debugger at all? Do you type something into it that triggers this exception?

[anjakefala]

Oh, this might be a Python version thing! I see you are using Python 3.9, which I am not!

[anjakefala]

Update I still cannot reproduce this with Python3.9. Waiting on more information or until I take the time to ensure my 3.9 environment is isolated.

[ajkerrigan]

I ran into this a while back too. It depended on my config and/or what I was doing in though debugger though - one reliable way to reproduce it was pip installing pdb++ and then triggering a breakpoint(). pdb++ checked local variables right away where pdb on its own didn't.

I started working on a fix in #589 but it was wrong in a few ways (handy comments from @saulpw in there!). It was fairly low priority for me and didn't seem to affect anyone else so I kinda left it hanging :grimacing: . @jasonwirth's approach sounds simpler though - fix the immediate ouch :).

[jasonwirth]

I did some quick adhoc testing using py3.8. I think the bug is in pdb++, as @ajkerrigan suggested. Dropping into a regular pdb debugger works, but pdb++ gets the error with both 3.8 and 3.9.

Edit: I've tried a variety of things, manually setting breakpoints, using VS Code debugger, etc. I came across this #558 issue on how to debug VD which links to @ajkerrigan page on debugging. Those docs and and CTRL+E to get the stacktrace has been very helpful.

[saulpw]

Thanks everyone for investigating this! @jasonwirth's solution is good, though I think the locals should be used before objs, if the key is available, because any locals in e.g. a generator expression should be "more local" than the column values. Can you put together a PR?