Float conversion error in IDLE

[rhettinger]

I observed the following console traceback while running IDLE from the command line:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/tkinter/__init__.py", line 1948, in __call__
    return self.func(*args)
           ^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/tkinter/__init__.py", line 861, in callit
    func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/idlelib/codecontext.py", line 243, in timer_event
    self.update_code_context()
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/idlelib/codecontext.py", line 187, in update_code_context
    new_topvisible = self.editwin.getlineno("@0,0")
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/idlelib/editor.py", line 1056, in getlineno
    return int(float(text.index(mark)))
               ^^^^^^^^^^^^^^^^^^^^^^^
ValueError: could not convert string to float: ''

[JamesParrott]

Hi Raymond. This puzzled me at first, but it's from a call to tkinter.Text.index (not str.index).

tkinter.Text.index can return a string, of the form "line.column", which could be coerced to a float, and thence the integer part extracted for the line number, just as in your error: int(float(text.index(mark))). A basic example can be tried out from the repl:

>>> import tkinter
>>> t = tkinter.Text()
>>> t.index('@0,0')
'1.0'

"@0,0" seems to be common notation in idlelib for a reference, that maybe was assumed to always return "line.column", when in your experience it didn't. But tkinter.Text.index can return all manner of other strings too, many of which are not convertable to floats, such as "line.end":

"The index notation for Text widgets is very rich and is best described in the Tk man pages."
https://docs.python.org/3/library/tkinter.html
https://tkdocs.com/shipman/text-index.html

Did you open a particular file with idlelib, or perform some particular action that caused this error?

[JamesParrott]

getlineno is intended to simply return a line number.
Perhaps delving into Tkinter and idlelib further is overthinking it, when a simple fix will probably suffice:

def getlineno(self, mark="insert"):
          text = self.text

 -        return int(float(text.index(mark)))
 +       text_widget_index = text.index(mark)
 +       return int(text_widget_index.partition('.')[0])

32152cf

[terryjreedy]

Raymond, is this, as far as you know, a unique occurrence for you? Traceback indicates Mac, as usual.
It seems that _tkinter.c catches and prints TclErrors in callbacks, allowing the program to continue as if the event never happened. I added an explicit raise and got a similar traceback. Your traceback does not include toggle_code_context, so the initial update call worked. A later timer update had the error.

Even though the index arg of text.index can have multiple forms, the return value is documented at https://www.tcl.tk/man/tcl8.6/TkCmd/text.html#M130 as always having the form 'line.col'. The error message says that it was instead '', which is a ValueError for both float() and int(). Since ''.partition('.')[0] == '', it is no fix. Ditto for the more usual alternative ''.split('.')[0].

https://www.tcl.tk/man/tcl8.6/TkCmd/text.html#M24 says "@x,y: Indicates the character that covers the pixel whose x and y coordinates within the text's window are x and y. " AFAIK, index('@0,0') has been working for years. It is used in several places in editor.py. (CHECK: all in event handlers?) And as noted above, I believe it worked at least once in Raymond's session. It is hard to know, for instance, if @1,1 would work better.

Under what condition does it return '' instead of the documented value? I tried showing code context in a blank IDLE editor started from Command Prompt (Windows) and Terminal and got no error in multiple tries.

EDIT: close was accident

[rhettinger]

I don't have any additional information on this. I run IDLE from the terminal using python3.11 -m idlelib.idle so that I and my students have control over the start-up directory. I leave it on while doing interesting Python demos all day long. At the end of the day when closing down, I saw this traceback and thought it might indicate a programming error. Most people never see these tracebacks because they aren't running from a terminal and stderr messages are lost. Also most people never exercise IDLE as heavily as I do.

[serhiy-storchaka]

Text.index() can return an empty string if the argument is invalid. And it is the first surprise, because in pure Tk shell it is an error. I have no idea why it is not a TclError in Tkinter.

In any case, it can return an empty string as an indication of some error. I was not able to get any error for "@0,0". I tried with freshly created text widget not yet managed by the geometry manager, I tried to move the window on other screen, to change the window size to zero, to withdraw and forget it -- nothing produced error. So we should just handle the special case of an empty string, return some sensible value from getlineno() which does not cause issues on the caller side.

[chrstphrchvz]

I looked into this issue a while ago, but neglected to comment here. I am not sure Tkinter should work around this, because from what I can tell, it is not expected behavior.

I asked on the Tcl chatroom (which I do not frequent) about how the text index command could return an empty string without error. One veteran Tcl/Tk maintainer replied that it should not be possible, nor were there any recent C code changes which would affect this. I agree with this assessment; if the text index command does not raise an error, then the result must have the form %d.%d, as this call chain in the C code should illustrate:
TextWidgetObjCmd() https://github.com/tcltk/tk/blob/core-8-6-13/generic/tkText.c#L1359
TkTextNewIndexObj() https://github.com/tcltk/tk/blob/core-8-6-13/generic/tkTextIndex.c#L285
UpdateStringOfTextIndex() https://github.com/tcltk/tk/blob/core-8-6-13/generic/tkTextIndex.c#L140
TkTextPrintIndex() https://github.com/tcltk/tk/blob/core-8-6-13/generic/tkTextIndex.c#L1131

This should also rule out the possibility of it returning e.g. something of the form %d.end.

However, because I mentioned that this was an isolated occurrence, someone else in the chatroom attributed the issue to a "cosmic ray" (i.e. single event upset).

[StanFromIreland]

I agree that this might just be a "cosmic ray".

Unable to reproduce on main branch build or 3.13.