Python standard library: pickletools

There's a crash bug in the in progress Stackless Python 3.1a2 release, but only on Linux. The particular use case, is where a tasklet is run for a very short time before being interrupted, pickled at its current point of execution, unpickled to a new version of the tasklet and then run. However, there appears to be some corruption in the pickling, which results in a recreated tasklet that appears to loop forever.

Now, the first step is to understand what pickle output. In the past, I've broken down the pickle strings into a readable form by hand. This time, I googled for "disassembling python pickle dump" and one of the first hits was pickletools. Now, this code appears to be somewhere within a Sourceforge repository, and I am too lazy to track it down, so I googled for "pickletools" and found it was now in the standard library for Python 2.6. Bingo!

Trying it out gives a dump which looks like this:

>>> pickletools.dis(s)
   0: \x80 PROTO      3
   2: c    GLOBAL     'stackless tasklet'
  21: q    BINPUT     0
  23: )    EMPTY_TUPLE
  24: R    REDUCE
  25: q    BINPUT     1
  27: (    MARK
  28: K        BININT1    8
  30: N        NONE
  31: K        BININT1    0
  33: ]        EMPTY_LIST
  34: q        BINPUT     2
  36: c        GLOBAL     'stackless._wrap frame'
  59: q        BINPUT     3
  61: c        GLOBAL     'stackless._wrap code'
  83: q        BINPUT     4
  85: (        MARK
  ...

Disassembling both the Linux and Windows pickle dumps of the tasklet, gives me the point at which they differ.

Windows:

  ...
  400: N            NONE
  401: N            NONE
  402: J            BININT     -1
  407: K            BININT1    4
  409: )            EMPTY_TUPLE
  ...

Linux:

  ...
  400: N            NONE
  401: N            NONE
  402: K            BININT1    31
  404: K            BININT1    4
  406: K            BININT1    120
  ...

Brilliant :-) This is a huge help and will save me a lot of time.