Peter Otten <[EMAIL PROTECTED]> wrote:
>> Which version of Python, and what happens when you try it?
>>
>> It works fine for me with Python 2.5 on Windows:
>>
>> C:\Temp>\python25\python -m pdb t.py
>>> c:\temp\t.py(3)<module>()
>> -> a = 1
>> (Pdb) s
>>> c:\temp\t.py(4)<module>()
>> -> b = 2
>> (Pdb) j 3
>>> c:\temp\t.py(3)<module>()
>> -> a = 1
>> (Pdb)
>
> It looks like you successfully jumped to the first line, but it will
be
> skipped if you try to execute it:
>
That's why I asked what actually happened. Yes, you and the OP seem to
be correct, jumping to the first executable line in a module appears not
to execute the line.
I verified (with a print statement in pdb) that assigning to
self.curframe.f_lineno sets self.curframe.f_lineno and
sel.curframe.f_lasti incorrectly:
C:\Temp>\python25\python -m pdb t.py
> c:\temp\t.py(3)<module>()
-> a = 1
(Pdb) s
> c:\temp\t.py(4)<module>()
-> b = 2
(Pdb) s
> c:\temp\t.py(5)<module>()
-> a = 3
(Pdb) l
1 #!/usr/bin/env python
2
3 a = 1
4 b = 2
5 -> a = 3
6 c = a + b
7 import dis, sys
8 dis.dis(sys._getframe().f_code)
9 print c
[EOF]
(Pdb) j 4
f_lineno 4 f_lasti 6
> c:\temp\t.py(4)<module>()
-> b = 2
(Pdb) j 3
f_lineno 4 f_lasti 6
> c:\temp\t.py(3)<module>()
-> a = 1
(Pdb) j 5
f_lineno 5 f_lasti 12
> c:\temp\t.py(5)<module>()
-> a = 3
(Pdb) j 3
f_lineno 4 f_lasti 6
> c:\temp\t.py(3)<module>()
-> a = 1
(Pdb)
The problem looks to be in frameobject.c:
addr = 0;
line = f->f_code->co_firstlineno;
new_lasti = -1;
for (offset = 0; offset < lnotab_len; offset += 2) {
addr += lnotab[offset];
line += lnotab[offset+1];
if (line >= new_lineno) {
new_lasti = addr;
new_lineno = line;
break;
}
}
The first bytes in lnotab are the length and line increment for line 3
(i.e. 6, 1). If line==f->f_code->co_firstlineno it should set new_lasti=
0, new_lineno=line but the loop still executes once which increments
new_lasti and new_lineno to the next line (6, 4).
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