Hopefully I\'m reading this wrong but in the XGBoost library documentation, there is note of extracting the feature importance attributes using feature_importances_
For those having the same problem as Luís Bianchin, "TypeError: 'str' object is not callable", I found a solution (that works for me at least) here.
In short, I found modifying David's code from
imp_vals = xgb.booster().get_fscore()
to
imp_vals = xgb.get_fscore()
worked for me.
For more detail I would recommend visiting the link above.
Big thanks to David and ianozsvald