load_word2vec_format(): new parameter to skip init_sims() call

[svenkreiss]

In certain use cases (custom doc2vec-type computations) only unnormalized vectors are used. The init_sims() call at the end of load_word2vec_format takes a lot of memory (even with norm_only=True) and is unnecessary in this scenario. This PR allows to skip the call which improves performance.

[piskvorky]

Sounds useful and clean, +1. A unit test for this new parameter would be useful.

Let's wait for @gojomo review & then merge.

[piskvorky]

Also @svenkreiss , can you commit a brief description of this change in CHANGELOG.txt?

[svenkreiss]

@piskvorky thanks for comments. Done.

[piskvorky]

Perfect, thanks a lot @svenkreiss !

[gojomo]

Looks fine, but another more radical simplification that reduces parameters & codepaths would also be worth considering: just don't do any automatic norming in the load_word2vec_format(). (That is, remove the init_sims() call rather than make it switchable.)

Then the (syn0) result of a load is really just a load, not a load-and-do-other stuff. This would also be roughly consistently with the syn0 state after native gensim training: you have the raw vectors, what you do with them next is up to your explicit further steps.

If the user starts making similarity calls, syn0norm would be automatically backfilled, as with natively-trained vectors.... but someone who doesn't need that would just choose not to trigger it.

If they instead want to convert to a compact, normed-only model, they'd call init_sims(norm_only=True) themself – just as if they'd trained the vectors with gensim (rather than just loaded).

[piskvorky]

Oh yes, that makes sense too. I actually like @gojomo 's option better -- simpler is better.

[svenkreiss]

I also agree with @gojomo. I can prepare a PR that removes the init_sims and norm_only parameters next week.

This would be api backwards incompatible and change the default behavior of this function.

[piskvorky]

Yes, we'll need a prominent warning in CHANGELOG :)

Thanks again @svenkreiss , you're really helpful!