Only calculate price ratios when company in key_ratios is demoninated in USD and allow specifying the specific exchange#50

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mwaldstein wants to merge 2 commits intobusiness-science:masterfrom mwaldstein:best_effort_key_ratios

+89-62

Commits on Jun 14, 2017

Modification to tq_get to allow fetching key ratios from arbitrary exchanges.
mwaldstein
committed

Commits on Jun 23, 2017

Allowed get='key.ratios' to specify the specific exchange to query and only calculate P/E if possible.
mwaldstein
committed