[Python-Dev] PEP 553: Built-in debug()

Terry Reedy tjreedy at udel.edu
Thu Sep 7 02:59:55 EDT 2017

On 9/6/2017 6:45 PM, Barry Warsaw wrote:
> On Sep 6, 2017, at 14:59, Terry Reedy <tjreedy at udel.edu> wrote:
>> Currently, the debugger is started in response to a menu seletion in the IDLE process while the python process is idle.  One reason for the 'idle' requirement' is because when code is exec-uting, the loop that reads commands, executes them, and sends responses is blocked on the exec call. The IDLE process sets up its debugger window, its ends of the rpc channels, and commands to python process to set up Idb and the other ends of the channels.  The challenge would be to initiate setup from the server process and deal with the blocked loop.
> Would the environment variable idea in the latest version of the PEP help you here?

That seems to be a mechanism for users to convey which function to call. 
  It does not simplify the function call chosen.

pdb works because a) it is designed to be imported into and run in a 
user module and b) it uses the existing stdin and stdout streams to 
interact with the user.  Idb, on the other hand, is designed to be 
import in idlelib.run, which is (almost) invisible to user code, and use 
a special channel to the GUI window.

Having said that, I see a solution: before running user code, set things 
up as now, except do not start tracing and do not show the debugger 
window, but do set a run.idb_ready flag.   Then breakpoint_handler() can 
check the flag and start tracing either through idb or pdb.

What makes breakpoint() less than super useful in IDLE is that IDLE 
already allows setting of persistent breakpoints on a line by 
right-clicking.  Since they are not stored in the file, there is nothing 
to erase when one runs the code in Python directly.

Terry Jan Reedy

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