Hello,

with python 2.7 I encounter the following problem:
I have created the following sample script:

import pdb

def function_1(number):
    stack_1 = number
    function_2(stack_1)
    
def function_2(number):
    stack_2 = number + 1
    function_3(stack_2)
    
def function_3(number):
    stack_3 = number + 1
    pdb.set_trace()
    print stack_3
    
function_1(1)

This is what I have done in the pdb session:
> c:\tst_pdb.py(14)function_3()
-> print stack_3
(Pdb) l
  9         function_3(stack_2)
 10
 11     def function_3(number):
 12         stack_3 = number + 1
 13         pdb.set_trace()
 14  ->     print stack_3
 15
 16     function_1(1) [EOF]
(Pdb) stack_3
3
(Pdb) !stack_3 = 177
(Pdb) !print stack_3
177
(Pdb) u
> c:\tst_pdb.py(9)function_2()
-> function_3(stack_2)
(Pdb) l
  4         stack_1 = number
  5         function_2(stack_1)
  6
  7     def function_2(number):
  8         stack_2 = number + 1
  9  ->     function_3(stack_2)
 10
 11     def function_3(number):
 12         stack_3 = number + 1
 13         pdb.set_trace()
 14         print stack_3
(Pdb) !print stack_2
2
(Pdb) !stack_2 = 144
(Pdb) !print stack_2
144
(Pdb) d
> c:\tst_pdb.py(14)function_3()
-> print stack_3
(Pdb) l
  9         function_3(stack_2)
 10
 11     def function_3(number):
 12         stack_3 = number + 1
 13         pdb.set_trace()
 14  ->     print stack_3
 15
 16     function_1(1) [EOF]
(Pdb) stack_3
3
(Pdb) u
> c:\tst_pdb.py(9)function_2()
-> function_3(stack_2)
(Pdb) !print stack_2
2
(Pdb)

I walked through the stack and changed the values of the variables stack_x but the values weren't saved when I moved one frame up/down

Thank you for the report. I don’t know pdb much, but I assume you have checked the doc to make sure this is indeed a bug. Can you test it with 3.1 and 3.2 too?

Bug tracker tip: You can find if a core developer is interested in a module in Misc/maintainers.rst and make them nosy (or assign to them, if there is a star near their name, like in Georg’s case).

The problem here is that changes in the locals are only saved back to the frame when leaving the trace function, and up/down don't do that.

This could be fixed by making Pdb.curframe_locals a dictionary for all visited frames while interaction is running.  I'll look into it for 3.2.

I believe this is slightly tricky because 'bdb.format_stack_entry' makes references to '.f_locals' and 'bdb.format_stack_entry' is invoked in several places in 'pdb'.  One option would be to add a extra parameter to 'bdb.format_stack_entry' to accept a dictionary of locals to operate with.

I implemented this approach and added a doctest to verify.  See attached patch.  I didn't update the 'bdb' documentation to note the new parameter, but will if this approach seems reasonable.