limitations of new multiline code and closure support in pdb

[limwz01]

Bug report

Bug description:

The following code is the template to illustrate the problems:

#!/usr/bin/env python3.13
g0 = 0
def main():
    import pdb
    pdb.Pdb().set_trace()
if __name__ == "__main__":
    main()

The problems:

• not re-using the same Cells for each local (this is really the biggest issue)

  (Pdb) t = 1
  (Pdb) f = lambda: t
  (Pdb) t = 2
  (Pdb) f()
  1

• not obtaining the last expression (a pdb test suggests otherwise, but it is actually wrong)

  (Pdb) t=10; (lambda: t)()
  <no output>

  (it does return a value for global g; g=1; g. but I'm at a loss as to where that value comes from)

• giving a weird result with shadowed variables (actually because it bails out):

  (Pdb) g0 = 1
  (Pdb) global g0; t=g0; t=(lambda: t)()
  *** NameError: name 't' is not defined

• not removing annotations (not allowed for nonlocal variables)

  (Pdb) t:int = 1; (lambda: t)()
  *** NameError: name 't' is not defined

• using indentation to set up block scope

  (Pdb) print((lambda:len("""
  ... """))())
  7

• not remembering globals (this is arguable):

  (Pdb) global g; g=1
  (Pdb) t=2
  (Pdb) g=(lambda: t)()
  (Pdb) global g; g
  1

  @gaogaotiantian

CPython versions tested on:

3.13

Operating systems tested on:

Linux

[limwz01]

An approach similar to mine at https://github.com/limwz01/ipython_utils and published at https://pypi.org/project/ipython-utils/ might help here. My code is very complicated but that's also because I wanted to support dynamic reloading of the code after an exception.

[gaogaotiantian]

Thank you for the detailed report and the many test cases. Like I said in the other issue, we might not be able to fix all of them, but I'll see if there's something cheap and readable thing I can do to fix some of these!