Hi all,

the current implementations of pdist and cdist takes as keyword arguments some extra parameters for a few specific metrics. At the same time, they do not allow for others args/kwargs that may be needed by a new user-defined metric.
Plus, in 0.19 it is possible to call:

pdist([[1,2,3]], metric='euclidean', V=[1,2,3], w=[1,2,3])
pdist([[1,2,3]], metric='seuclidean', VI=[1,2,3])

IMHO this is quite strange behaviour since I would have expected an error.
In particular, in the second case, the error would also probably help debugging the code since it may be a copy-and-paste typo (seuclidean takes V as kwarg, while mahalanobis requires VI)

I have opened a PR (https://github.com/scipy/scipy/pull/6974) that introduces support for *args and **kwargs that gets passed on to the selected metric. The new functions should not break any existing code with the exception of the previous example.
However, if needed, I can try to catch those cases, and for now just raise a deprecate warning.

what do you think?

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