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In the following test both breakpoints are set on the line of a
function definition. However pdb does not stop when entering foo whose
breakpoint has been set with 'break 1' while pdb stops when entering
bar whose breakpoint has been set with 'break bar'. The breakpoint
table display is identical for both breakpoints. This is inconsistent
and confusing.
=== main.py ==================================
1 def foo():
2 pass
3
4 def bar():
5 pass
6
7 def main():
8 foo()
9 bar()
10
11 import pdb; pdb.runcall(main)
=================================================
$ python main.py
> /path_to/main.py(8)main()
-> foo()
(Pdb) break 1
Breakpoint 1 at /path_to/main.py:1
(Pdb) break bar
Breakpoint 2 at /path_to/main.py:4
(Pdb) break
Num Type Disp Enb Where
1 breakpoint keep yes at /path_to/main.py:1
2 breakpoint keep yes at /path_to/main.py:4
(Pdb) continue
> /path_to/main.py(5)bar()
-> pass
(Pdb) continue
$
=================================================
The reverse occurs in the following test where pdb stops only at the
execution of the function definition when the breakpoint has been set
with a line number.
=== main.py ==================================
 1 x = 1
 2
 3 def foo():
 4 pass
 5
 6 def bar():
 7 pass
 8
 9 x = 2
=================================================
$ python -m pdb main.py
> /path_to/main.py(1)<module>()
-> x = 1
(Pdb) break 3
Breakpoint 1 at /path_to/main.py:3
(Pdb) break bar
Breakpoint 2 at /path_to/main.py:6
(Pdb) break 9
Breakpoint 3 at /path_to/main.py:9
(Pdb) break
Num Type Disp Enb Where
1 breakpoint keep yes at /path_to/main.py:3
2 breakpoint keep yes at /path_to/main.py:6
3 breakpoint keep yes at /path_to/main.py:9
(Pdb) continue
> /path_to/main.py(3)<module>()
-> def foo():
(Pdb) continue
> /path_to/main.py(9)<module>()
-> x = 2
(Pdb)
=================================================
The following patch fixes both inconsistencies by having pdb stop when
entering a function and at the execution of a definition whatever the
method used to set the breakpoint (line number or function name).
Two test cases are included in the patch.

Parsing the modules source seems a better way to fix this problem, see issue 14913.