[Python-Dev] Status of dictnotes.txt?

Brendan O'Connor brenocon at gmail.com
Tue Sep 23 19:34:09 CEST 2008

> If I remember correctly (and based on a skimming of dictnotes.txt),
> those aren't suggestions, it is documentation about the actual
> implementation and why those decisions were made.

Well, some of the document is written as "if we did X, then we'd see
Y" so it's not always clear.  Some parts are clearly not implemented,
e.g. read-only freezing.  Some parts are implemented but slightly
differently -- e.g. small dicts are specialized to be faster, but the
document talks about specializing lookdict() and lookdict_string()
with linear search; however, as far as I can tell,
PyDictObject->ma_smalltable is used for small dictionaries, with the
standard hashing algorithm.

This is a little confusing because the ma_lookup() function pointer is
used as indirection; I was thinking that maybe there was a linear
search version, but actually it looks like it's just set to
lookdict_string() then switches to lookdict() if there's ever a
non-string key.  lookdict[_string]() always uses hashing.

Anyway, if anyone who knows about this or dictnotes.txt in general is
reading, feel free to pipe in :)


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