[PYTHON-DIST] Distributed xgboost python training API.

include/xgboost/learner.h

@@ -109,6 +109,21 @@ class Learner : public rabit::Serializable {
                        std::vector<float> *out_preds,
                        unsigned ntree_limit = 0,
                        bool pred_leaf = false) const = 0;
+  /*!
+   * \brief Set additional attribute to the Booster.
+   *  The property will be saved along the booster.
+   * \param key The key of the property.
+   * \param value The value of the property.
+   */
+  virtual void SetAttr(const std::string& key, const std::string& value) = 0;
+  /*!
+   * \brief Get attribute from the booster.
+   *  The property will be saved along the booster.
+   * \param key The key of the attribute.
+   * \param out The output value.
+   * \return Whether the key is contained in the attribute.
+   */
+  virtual bool GetAttr(const std::string& key, std::string* out) const = 0;
   /*!
    * \return whether the model allow lazy checkpoint in rabit.
    */