[Python-Dev] The memo of pickle

[Martin v. Loewis]

Guido van Rossum <guido@python.org> writes:

> Is it worth it?  

If you believe that the problem is real, yes.

> Have you made a patch?  

Not yet, no. With Mark's objection, it is more difficult than I
thought.

> What use case are you thinking of?

People repeatedly complain that pickle consumes too much memory. The
most recent instance was

http://groups.google.de/groups?selm=slrnal05v1.c05.Andreas.Leitgeb%40pc7499.gud.siemens.at&output=gplain

Earlier reports are

http://groups.google.de/groups?hl=de&lr=&ie=UTF-8&selm=mailman.1026940226.16076.python-list%40python.org

http://groups.google.de/groups?q=pickle+memory+group:comp.lang.python.*&hl=de&lr=&ie=UTF-8&selm=396B069A.9EBDD68B%40muc.das-werk.de&rnum=4

> Sorry, what's an identity dict?

IdentityDictionary is the name of a Smalltalk class that uses identity
instead of equality when comparing keys:

http://minnow.cc.gatech.edu/squeak/1845

In Python, it would allow arbitrary objects as keys, and allow equal
duplicates as different keys. For pickle, this would mean that we
could save both the creation of the id() object (since the object
itself is used as a key), and the creation of the tuple (since the
value is only the position).

Regards,
Martin