[Python-Dev] Should there be a source-code checksum in module objects? (original) (raw)

Guido van Rossum guido at python.org
Mon Feb 2 20:01:56 CET 2009

On Mon, Feb 2, 2009 at 10:48 AM, <rocky at gnu.org> wrote:

Brett Cannon writes: > On Mon, Feb 2, 2009 at 00:52, Rocky Bernstein <rocky at gnu.org> wrote: > > As I've mentioned, I've been re-examining from ground up the whole > > state of affairs in writing a debugger. > > > > One of the challenges of a debugger or any source-code analysis tool > > is verifying that the source-code that the tool is reporting on > > corresponds to the compiled object under execution. (For debuggers, > > this problem becomes more likely to occur when you are debugging on a > > computer that isn't the same as the computer where the code is > > running.) > > > > Is there a checksum of the source text computed and stored in > > compilation? > > No, only the bytecode version used, the mtime of the source the > bytecode is derived from, and the bytecode itself. > > > If not, should there be one? > > If you are planning to read this directly from the .pyc file then it > is not needed as the mtime timestamp in the .pyc should in general be > enough to detect changes to the source.

I'm not sure I understand. I am debugging program P on computer A which may have (probably did?) do a compile. I am on computer B which I have the source code. Maybe it is checked out from a version control system same as on A. Maybe it has bytecodes, maybe not. But the expectation is that the programmer thinks it matches what is currently on A that the programmer is debuggging. Can I tell for certain? Suppose I'm writing a code coverage tool which can accumulate statistics over many runs. I notice that the date on the Python file changes, again one way it might is that it might be checked out fresh and subversion for example will put in a current timestamp. How can the code coverage tool know that the source hasn't changed even though the file may have disappeared or maybe was modified several times but in the end stays the same?

Unfortunately this use case (remote debugging) was not considered when the code object was designed and implemented. I don't know how important the use case is in general, but clearly it is important to you.

I suggest that you move this discussion to python-ideas to ferret out a possible implementation and API; or to find out work-arounds.

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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