To whom he want to set breakpoint on negative line number in pdb

[Jach Feng]

I use .pdbrc file to help debugging. To avoid editing this file frequently when source was modified, I need this feature.

I modify the checkline function in pdb.py from
    ...
    line = linecache.getline(filename, lineno, globs)
    if not line:
        ....
to
    ...
    lines = linecache.getlines(filename, globs)
    if lineno < 0:  lineno = len(lines) + lineno + 1  # change to a valid positive number, or not
    if 1 <= lineno <= len(lines):  line = lines[lineno-1]
    else:  line = ''
    if not line:
        ...

This modification is mostly the copy of the getline function body except the added line. It will not influence the original pdb usage in anyway.

--Jach