Merge pull request #97 from wxchan/dev

Clean codes for python-package; dump model to JSON

README.md

@@ -17,7 +17,7 @@ For more details, please refer to [Features](https://github.com/Microsoft/LightG
 News
 ----
 
-12/02/2012 : Release [python-package](https://github.com/Microsoft/LightGBM/tree/master/python-package) beta version, welcome to have a try and provide issues and feedback.
+12/02/2016 : Release [python-package](https://github.com/Microsoft/LightGBM/tree/master/python-package) beta version, welcome to have a try and provide issues and feedback.
 
 Get Started
 ------------

examples/python-guide/README.md

+Python Package Example
+=====================
+Here is an example for LightGBM to use python package.
+
+***You should install lightgbm (both c++ and python verion) first.***
+
+For the installation, check the wiki [here](https://github.com/Microsoft/LightGBM/wiki/Installation-Guide).
+
+You also need scikit-learn and pandas to run the examples, but they are not required for the package itself. You can install them with pip:
+```
+pip install -U scikit-learn
+pip install -U pandas
+```
+
+Now you can run examples in this folder, for example:
+```
+python simple_example.py
+```

examples/python-guide/simple_example.py

-import numpy as np
-import random
+# coding: utf-8
+# pylint: disable = invalid-name, C0111
+import json
 import lightgbm as lgb
-from sklearn import datasets, metrics, model_selection
-
-rng = np.random.RandomState(2016)
-
-X, y = datasets.make_classification(n_samples=10000, n_features=100)
-x_train, x_test, y_train, y_test = model_selection.train_test_split(X, y, test_size=0.1, random_state=1)
-lgb_model = lgb.LGBMClassifier(n_estimators=100).fit(x_train, y_train, [(x_test, y_test)], eval_metric="auc")
-lgb_model.predict(x_test)
-# save model
-lgb_model.booster().save_model('model.txt')
-# load model
-booster = lgb.Booster(model_file='model.txt')
+import pandas as pd
+from sklearn.metrics import mean_squared_error
+
+# load or create your dataset
+df_train = pd.read_csv('../regression/regression.train', header=None, sep='\t')
+df_test = pd.read_csv('../regression/regression.test', header=None, sep='\t')
+
+y_train = df_train[0]
+y_test = df_test[0]
+X_train = df_train.drop(0, axis=1)
+X_test = df_test.drop(0, axis=1)
+
+# create dataset for lightgbm
+lgb_train = lgb.Dataset(X_train, y_train)
+lgb_eval = lgb.Dataset(X_test, y_test, reference=lgb_train)
+# or you can simply use a tuple of length=2 here
+lgb_train = (X_train, y_train)
+lgb_eval = (X_test, y_test)
+
+# specify your configurations as a dict
+params = {
+    'task' : 'train',
+    'boosting_type' : 'gbdt',
+    'objective' : 'regression',
+    'metric' : 'l2',
+    'num_leaves' : 31,
+    'learning_rate' : 0.05,
+    'feature_fraction' : 0.9,
+    'bagging_fraction' : 0.8,
+    'bagging_freq': 5,
+    # 'ndcg_eval_at' : [1, 3, 5, 10],
+    # this metric is not needed in this task, show as an example
+    'verbose' : 0
+}
+
+# train
+gbm = lgb.train(params,
+                lgb_train,
+                num_boost_round=100,
+                valid_datas=lgb_eval,
+                # you can use a list to represent multiple valid_datas/valid_names
+                # don't use tuple, tuple is used to represent one dataset
+                early_stopping_rounds=10)
+
+# save model to file
+gbm.save_model('model.txt')
+
+# load model from file
+gbm = lgb.Booster(model_file='model.txt')
+
 # predict
-print(booster.predict(x_test))
+y_pred = gbm.predict(X_test, num_iteration=gbm.best_iteration)
+# eval
+print('The rmse of prediction is:', mean_squared_error(y_test, y_pred) ** 0.5)
+
+# dump model to json (and save to file)
+model_json = gbm.dump_model()
+
+with open('model.json', 'w+') as f:
+    json.dump(model_json, f, indent=4)

examples/python-guide/sklearn_example.py

+# coding: utf-8
+# pylint: disable = invalid-name, C0111
+import lightgbm as lgb
+import pandas as pd
+from sklearn.metrics import mean_squared_error
+
+# load or create your dataset
+df_train = pd.read_csv('../regression/regression.train', header=None, sep='\t')
+df_test = pd.read_csv('../regression/regression.test', header=None, sep='\t')
+
+y_train = df_train[0]
+y_test = df_test[0]
+X_train = df_train.drop(0, axis=1)
+X_test = df_test.drop(0, axis=1)
+
+# train
+gbm = lgb.LGBMRegressor(objective='regression',
+                        num_leaves=31,
+                        learning_rate=0.05,
+                        n_estimators=100)
+gbm.fit(X_train, y_train,
+        eval_set=[(X_test, y_test)],
+        early_stopping_rounds=10)
+
+# predict
+y_pred = gbm.predict(X_test, num_iteration=gbm.best_iteration)
+# eval
+print('The rmse of prediction is:', mean_squared_error(y_test, y_pred) ** 0.5)

include/LightGBM/boosting.h

@@ -133,9 +133,16 @@ public:
     const double* feature_values) const = 0;
 
   /*!
-  * \brief save model to file
-  * \param num_iterations Iterations that want to save, -1 means save all
-  * \param filename filename that want to save to
+  * \brief Dump model to json format string
+  * \return Json format string of model
+  */
+  virtual std::string DumpModel() const = 0;
+
+  /*!
+  * \brief Save model to file
+  * \param num_used_model Number of model that want to save, -1 means save all
+  * \param is_finish Is training finished or not
+  * \param filename Filename that want to save to
   */
   virtual void SaveModelToFile(int num_iterations, const char* filename) const = 0;
 

include/LightGBM/c_api.h

@@ -474,7 +474,18 @@ DllExport int LGBM_BoosterSaveModel(BoosterHandle handle,
   int num_iteration,
   const char* filename);
 
-
+/*!
+* \brief dump model to json
+* \param handle handle
+* \param buffer_len string buffer length, if buffer_len < out_len, re-allocate buffer
+* \param out_len actual output length
+* \param out_str json format string of model
+* \return 0 when succeed, -1 when failure happens
+*/
+DllExport int LGBM_BoosterDumpModel(BoosterHandle handle,
+  int buffer_len,
+  int64_t* out_len,
+  char** out_str);
 
 // some help functions used to convert data
 

include/LightGBM/tree.h

@@ -98,9 +98,12 @@ public:
     }
   }
 
-  /*! \brief Serialize this object by string*/
+  /*! \brief Serialize this object to string*/
   std::string ToString();
 
+  /*! \brief Serialize this object to json*/
+  std::string ToJSON();
+
 private:
   /*!
   * \brief Find leaf index of which record belongs by data
@@ -118,6 +121,9 @@ private:
   */
   inline int GetLeaf(const double* feature_values) const;
 
+  /*! \brief Serialize one node to json*/
+  inline std::string NodeToJSON(int index);
+
   /*! \brief Number of max leaves*/
   int max_leaves_;
   /*! \brief Number of current levas*/
@@ -137,13 +143,13 @@ private:
   std::vector<double> threshold_;
   /*! \brief A non-leaf node's split gain */
   std::vector<double> split_gain_;
+  /*! \brief Output of internal nodes(save internal output for per inference feature importance calc) */
+  std::vector<double> internal_value_;
   // used for leaf node
   /*! \brief The parent of leaf */
   std::vector<int> leaf_parent_;
   /*! \brief Output of leaves */
   std::vector<double> leaf_value_;
-  /*! \brief Output of internal nodes(save internal output for per inference feature importance calc) */
-  std::vector<double> internal_value_;
   /*! \brief Depth for leaves */
   std::vector<int> leaf_depth_;
 };

python-package/lightgbm/__init__.py

@@ -20,4 +20,5 @@ __version__ = 0.1
 
 __all__ = ['Dataset', 'Booster',
            'train', 'cv',
-           'LGBMModel','LGBMRegressor', 'LGBMClassifier', 'LGBMRanker']
\ No newline at end of file
+           'LGBMModel', 'LGBMRegressor', 'LGBMClassifier', 'LGBMRanker']
+

python-package/lightgbm/basic.py

+# coding: utf-8
+# pylint: disable = invalid-name, C0111, R0912, R0913, R0914, W0105
 """Wrapper c_api of LightGBM"""
 from __future__ import absolute_import
 
@@ -5,12 +7,24 @@ import sys
 import os
 import ctypes
 import tempfile
+import json
 
 import numpy as np
 import scipy.sparse
 
 from .libpath import find_lib_path
 
+# pandas
+try:
+    from pandas import Series, DataFrame
+    IS_PANDAS_INSTALLED = True
+except ImportError:
+    IS_PANDAS_INSTALLED = False
+    class Series(object):
+        pass
+    class DataFrame(object):
+        pass
+
 IS_PY3 = (sys.version_info[0] == 3)
 
 def _load_lib():
@@ -69,6 +83,8 @@ def list_to_1d_numpy(data, dtype):
             return data.astype(dtype=dtype, copy=False)
     elif is_1d_list(data):
         return np.array(data, dtype=dtype, copy=False)
+    elif IS_PANDAS_INSTALLED and isinstance(data, Series):
+        return data.astype(dtype).values
     else:
         raise TypeError("Unknow type({})".format(type(data).__name__))
 
@@ -367,13 +383,6 @@ class Predictor(object):
             raise ValueError("incorrect number for predict result")
         return preds, nrow
 
-# pandas
-try:
-    from pandas import DataFrame
-except ImportError:
-    class DataFrame(object):
-        pass
-
 PANDAS_DTYPE_MAPPER = {'int8': 'int', 'int16': 'int', 'int32': 'int',
                        'int64': 'int', 'uint8': 'int', 'uint16': 'int',
                        'uint32': 'int', 'uint64': 'int', 'float16': 'float',
@@ -830,6 +839,7 @@ class Booster(object):
         self.__is_manage_handle = True
         self.__train_data_name = "training"
         self.__attr = {}
+        self.best_iteration = -1
         params = {} if params is None else params
         if silent:
             params["verbose"] = 0
@@ -1098,6 +1108,34 @@ class Booster(object):
             num_iteration,
             c_str(filename)))
 
+    def dump_model(self):
+        """
+        Dump model to json format
+
+        Returns
+        -------
+        Json format of model
+        """
+        buffer_len = 1 << 20
+        tmp_out_len = ctypes.c_int64(0)
+        string_buffer = ctypes.create_string_buffer(buffer_len)
+        ptr_string_buffer = ctypes.c_char_p(*[ctypes.addressof(string_buffer)])
+        _safe_call(_LIB.LGBM_BoosterDumpModel(
+            self.handle,
+            buffer_len,
+            ctypes.byref(tmp_out_len),
+            ctypes.byref(ptr_string_buffer)))
+        actual_len = tmp_out_len.value
+        if actual_len > buffer_len:
+            string_buffer = ctypes.create_string_buffer(actual_len)
+            ptr_string_buffer = ctypes.c_char_p(*[ctypes.addressof(string_buffer)])
+            _safe_call(_LIB.LGBM_BoosterDumpModel(
+                self.handle,
+                actual_len,
+                ctypes.byref(tmp_out_len),
+                ctypes.byref(ptr_string_buffer)))
+        return json.loads(string_buffer.value.decode())
+
     def predict(self, data, num_iteration=-1, raw_score=False, pred_leaf=False, data_has_header=False, is_reshape=True):
         """
         Predict logic
@@ -1190,7 +1228,7 @@ class Booster(object):
                 ctypes.byref(tmp_out_len),
                 data_ptr))
             if tmp_out_len.value != len(self.__inner_predict_buffer[data_idx]):
-                raise ValueError("incorrect number of predict results for data %d" % (data_idx) )
+                raise ValueError("incorrect number of predict results for data %d" % (data_idx))
             self.__is_predicted_cur_iter[data_idx] = True
         return self.__inner_predict_buffer[data_idx]
 

python-package/lightgbm/callback.py

+# coding: utf-8
+# pylint: disable = invalid-name, W0105
 from __future__ import absolute_import
 import collections
 
@@ -25,12 +27,12 @@ CallbackEnv = collections.namedtuple(
 def _format_eval_result(value, show_stdv=True):
     """format metric string"""
     if len(value) == 4:
-        return '%s_%s:%g' % (value[0], value[1], value[2])
+        return '%s\'s %s:%g' % (value[0], value[1], value[2])
     elif len(value) == 5:
         if show_stdv:
-            return '%s_%s:%g+%g' % (value[0], value[1], value[2], value[4])
+            return '%s\'s %s:%g+%g' % (value[0], value[1], value[2], value[4])
         else:
-            return '%s_%s:%g' % (value[0], value[1], value[2])
+            return '%s\'s %s:%g' % (value[0], value[1], value[2])
     else:
         raise ValueError("wrong metric value")
 
@@ -55,9 +57,10 @@ def print_evaluation(period=1, show_stdv=True):
         """internal function"""
         if len(env.evaluation_result_list) == 0 or period is False:
             return
-        if (env.iteration % period == 0 or env.iteration + 1 == env.begin_iteration):
-            result = '\t'.join([_format_eval_result(x, show_stdv) for x in env.evaluation_result_list])
-            print('[%d]\t%s\n' % (env.iteration, result))
+        if env.iteration % period == 0 or env.iteration + 1 == env.begin_iteration:
+            result = '\t'.join([_format_eval_result(x, show_stdv) \
+                for x in env.evaluation_result_list])
+            print('[%d]\t%s' % (env.iteration, result))
     return callback
 
 
@@ -137,7 +140,7 @@ def early_stop(stopping_rounds, verbose=True):
 
     Parameters
     ----------
-    stopp_rounds : int
+    stopping_rounds : int
        The stopping rounds before the trend occur.
 
     verbose : optional, bool
@@ -154,13 +157,11 @@ def early_stop(stopping_rounds, verbose=True):
     best_msg = {}
     def init(env):
         """internal function"""
-        bst = env.model
-
         if len(env.evaluation_result_list) == 0:
             raise ValueError('For early stopping you need at least one set in evals.')
 
         if verbose:
-            msg = "Will train until hasn't improved in {} rounds.\n"
+            msg = "Train until valid scores didn't improve in {} rounds."
             print(msg.format(stopping_rounds))
 
         for i in range(len(env.evaluation_result_list)):
@@ -182,13 +183,13 @@ def early_stop(stopping_rounds, verbose=True):
                 best_score[i] = score
                 best_iter[i] = env.iteration
                 if verbose:
-                    best_msg[i] = '[%d]\t%s' % ( env.iteration,
+                    best_msg[i] = '[%d]\t%s' % (env.iteration, \
                         '\t'.join([_format_eval_result(x) for x in env.evaluation_result_list]))
             else:
                 if env.iteration - best_iter[i] >= stopping_rounds:
                     if env.model is not None:
                         env.model.set_attr(best_iteration=str(best_iter[i]))
                     if verbose:
-                        print('early stopping, best message is:\n {} '.format(best_msg[i]))
+                        print('early stopping, best iteration is:\n{}'.format(best_msg[i]))
                     raise EarlyStopException(best_iter[i])
     return callback

python-package/lightgbm/engine.py

+# coding: utf-8
+# pylint: disable = invalid-name, W0105
 """Training Library containing training routines of LightGBM."""
 from __future__ import absolute_import
 
@@ -33,7 +35,6 @@ def _construct_dataset(X_y, reference=None,
         ret = Dataset(data, label=label, max_bin=max_bin,
                       weight=weight, group=group,
                       predictor=predictor, params=params)
-
     else:
         ret = reference.create_valid(data, label=label, weight=weight,
                                      group=group, params=params)
@@ -53,11 +54,11 @@ def train(params, train_data, num_boost_round=100,
     ----------
     params : dict
          params.
-    train_data : pair, (X, y) or filename of data
+    train_data : Dataset, tuple (X, y) or filename of data
         Data to be trained.
     num_boost_round: int
         Number of boosting iterations.
-    valid_datas: list of pairs (valid_X, valid_y) or filename of data
+    valid_datas: list of Datasets, tuples (valid_X, valid_y) or filename of data
         List of data to be evaluated during training
     valid_names: list of string
         names of valid_datas
@@ -72,7 +73,8 @@ def train(params, train_data, num_boost_round=100,
         other data file in training data. e.g. train_fields['weight'] is weight data
         support fields: weight, group, init_score
     valid_fields : dict
-        other data file in training data. e.g. valid_fields[0]['weight'] is weight data for first valid data
+        other data file in training data. \
+        e.g. valid_fields[0]['weight'] is weight data for first valid data
         support fields: weight, group, init_score
     early_stopping_rounds: int
         Activates early stopping.
@@ -82,8 +84,8 @@ def train(params, train_data, num_boost_round=100,
         If early stopping occurs, the model will add 'best_iteration' field
     evals_result: dict or None
         This dictionary used to store all evaluation results of all the items in valid_datas.
-        Example: with a valid_datas containing [valid_set, train_set] and valid_names containing ['eval', 'train'] and
-        a paramater containing ('metric':'logloss')
+        Example: with a valid_datas containing [valid_set, train_set] \
+        and valid_names containing ['eval', 'train'] and a paramater containing ('metric':'logloss')
         Returns: {'train': {'logloss': ['0.48253', '0.35953', ...]},
                   'eval': {'logloss': ['0.480385', '0.357756', ...]}}
         passed with None means no using this function
@@ -120,22 +122,32 @@ def train(params, train_data, num_boost_round=100,
     else:
         predictor = None
     """create dataset"""
+    if isinstance(train_data, Dataset):
+        train_set = train_data
+    else:
         train_set = _construct_dataset(train_data, None, params, train_fields, predictor)
     is_valid_contain_train = False
     train_data_name = "training"
     valid_sets = []
     name_valid_sets = []
     if valid_datas is not None:
-        for i in range(len(valid_datas)):
+        if isinstance(valid_datas, (Dataset, tuple)):
+            valid_datas = [valid_datas]
+        if isinstance(valid_names, str):
+            valid_names = [valid_names]
+        for i, valid_data in enumerate(valid_datas):
             other_fields = None if valid_fields is None else valid_fields[i]
             """reduce cost for prediction training data"""
-            if valid_datas[i] is train_data:
+            if valid_data is train_data:
                 is_valid_contain_train = True
                 if valid_names is not None:
                     train_data_name = valid_names[i]
                 continue
+            if isinstance(valid_data, Dataset):
+                valid_set = valid_data
+            else:
                 valid_set = _construct_dataset(
-                valid_datas[i],
+                    valid_data,
                     train_set,
                     params,
                     other_fields,
@@ -178,8 +190,8 @@ def train(params, train_data, num_boost_round=100,
     booster = Booster(params=params, train_set=train_set)
     if is_valid_contain_train:
         booster.set_train_data_name(train_data_name)
-    for i in range(len(valid_sets)):
-        booster.add_valid(valid_sets[i], name_valid_sets[i])
+    for valid_set, name_valid_set in zip(valid_sets, name_valid_sets):
+        booster.add_valid(valid_set, name_valid_set)
     """start training"""
     for i in range(num_boost_round):
         for cb in callbacks_before_iter:
@@ -209,9 +221,9 @@ def train(params, train_data, num_boost_round=100,
         except callback.EarlyStopException:
             break
     if booster.attr('best_iteration') is not None:
-        booster.best_iteration = int(booster.attr('best_iteration'))
+        booster.best_iteration = int(booster.attr('best_iteration')) + 1
     else:
-        booster.best_iteration = num_boost_round - 1
+        booster.best_iteration = num_boost_round
     return booster
 
 
@@ -233,12 +245,13 @@ class CVBooster(object):
         return self.booster.eval_valid(feval)
 
 try:
-    try:
-        from sklearn.model_selection import KFold, StratifiedKFold
-    except ImportError:
-        from sklearn.cross_validation import KFold, StratifiedKFold
+    from sklearn.model_selection import StratifiedKFold
     SKLEARN_StratifiedKFold = True
 except ImportError:
+    try:
+        from sklearn.cross_validation import StratifiedKFold
+        SKLEARN_StratifiedKFold = True
+    except ImportError:
         SKLEARN_StratifiedKFold = False
 
 def _make_n_folds(full_data, nfold, param, seed, fpreproc=None, stratified=False):
@@ -270,7 +283,6 @@ def _make_n_folds(full_data, nfold, param, seed, fpreproc=None, stratified=False
     return ret
 
 def _agg_cv_result(raw_results):
-    # pylint: disable=invalid-name
     """
     Aggregate cross-validation results.
     """
@@ -294,7 +306,6 @@ def cv(params, train_data, num_boost_round=10, nfold=5, stratified=False,
        metrics=(), fobj=None, feval=None, train_fields=None, early_stopping_rounds=None,
        fpreproc=None, verbose_eval=None, show_stdv=True, seed=0,
        callbacks=None):
-    # pylint: disable = invalid-name
     """Cross-validation with given paramaters.
 
     Parameters
@@ -351,7 +362,7 @@ def cv(params, train_data, num_boost_round=10, nfold=5, stratified=False,
     if isinstance(params, list):
         params = dict(params)
 
-    if not 'metric' in params:
+    if 'metric' not in params:
         params['metric'] = []
     else:
         if is_str(params['metric']):
@@ -410,7 +421,7 @@ def cv(params, train_data, num_boost_round=10, nfold=5, stratified=False,
                                         end_iteration=num_boost_round,
                                         evaluation_result_list=res))
         except callback.EarlyStopException as e:
-            for k in results.keys():
+            for k in results:
                 results[k] = results[k][:(e.best_iteration + 1)]
             break
     return results

python-package/lightgbm/libpath.py

+# coding: utf-8
+"""Find the path to lightgbm dynamic library files."""
 import os
-import platform
 import sys
 
 

python-package/lightgbm/sklearn.py

+# coding: utf-8
+# pylint: disable = invalid-name, W0105
 """Scikit-Learn Wrapper interface for LightGBM."""
 from __future__ import absolute_import
 
@@ -220,7 +222,8 @@ class LGBMModel(LGBMModelBase):
             other data file in training data. e.g. train_fields['weight'] is weight data
             support fields: weight, group, init_score
         valid_fields : dict
-            other data file in training data. e.g. valid_fields[0]['weight'] is weight data for first valid data
+            other data file in training data. \
+            e.g. valid_fields[0]['weight'] is weight data for first valid data
             support fields: weight, group, init_score
         other_params: dict
             other parameters
@@ -235,6 +238,13 @@ class LGBMModel(LGBMModelBase):
             params["objective"] = "None"
         else:
             params["objective"] = self.objective
+            if eval_metric is None and eval_set is not None:
+                eval_metric = {
+                    'regression': 'l2',
+                    'binary': 'binary_logloss',
+                    'lambdarank': 'ndcg',
+                    'multiclass': 'multi_logloss'
+                }.get(self.objective, None)
 
         if callable(eval_metric):
             feval = eval_metric
@@ -249,7 +259,8 @@ class LGBMModel(LGBMModelBase):
                               self.n_estimators, valid_datas=eval_set,
                               early_stopping_rounds=early_stopping_rounds,
                               evals_result=evals_result, fobj=self.fobj, feval=feval,
-                              verbose_eval=verbose, train_fields=train_fields, valid_fields=valid_fields)
+                              verbose_eval=verbose, train_fields=train_fields,
+                              valid_fields=valid_fields)
 
         if evals_result:
             for val in evals_result.items():
@@ -320,14 +331,18 @@ class LGBMClassifier(LGBMModel, LGBMClassifierBase):
             # Switch to using a multiclass objective in the underlying LGBM instance
             self.objective = "multiclass"
             other_params['num_class'] = self.n_classes_
+            if eval_metric is None and eval_set is not None:
+                eval_metric = "multi_logloss"
         else:
             self.objective = "binary"
+            if eval_metric is None and eval_set is not None:
+                eval_metric = "binary_logloss"
 
         self._le = LGBMLabelEncoder().fit(y)
         training_labels = self._le.transform(y)
 
         if eval_set is not None:
-            eval_set = list( (x[0], self._le.transform(x[1])) for x in eval_set )
+            eval_set = list((x[0], self._le.transform(x[1])) for x in eval_set)
 
         super(LGBMClassifier, self).fit(X, training_labels, eval_set,
                                         eval_metric, early_stopping_rounds,
@@ -430,6 +445,8 @@ class LGBMRanker(LGBMModel):
         else:
             self.objective = "lambdarank"
             self.fobj = None
+            if eval_metric is None and eval_set is not None:
+                eval_metric = "ndcg"
 
         super(LGBMRanker, self).fit(X, y, eval_set, eval_metric,
                                     early_stopping_rounds, verbose,

python-package/setup.py

+# coding: utf-8
 # pylint: disable=invalid-name, exec-used
 """Setup lightgbm package."""
 from __future__ import absolute_import

src/boosting/gbdt.cpp

@@ -393,6 +393,36 @@ void GBDT::Boosting() {
     GetGradients(GetTrainingScore(&num_score), gradients_.data(), hessians_.data());
 }
 
+std::string GBDT::DumpModel() const {
+  std::stringstream ss;
+
+  ss << "{";
+  ss << "\"name\":\"" << Name() << "\"," << std::endl;
+  ss << "\"num_class\":" << num_class_ << "," << std::endl;
+  ss << "\"label_index\":" << label_idx_ << "," << std::endl;
+  ss << "\"max_feature_idx\":" << max_feature_idx_ << "," << std::endl;
+  if (object_function_ != nullptr) {
+    ss << "\"objective\":\"" << object_function_->GetName() << "\"," << std::endl;
+  }
+  ss << "\"sigmoid\":" << sigmoid_ << "," << std::endl;
+
+  ss << "\"tree_info\":[";
+  for (int i = 0; i < static_cast<int>(models_.size()); ++i) {
+    if (i > 0) {
+      ss << ",";
+    }
+    ss << "{";
+    ss << "\"tree_index\":" << i << ",";
+    ss << models_[i]->ToJSON();
+    ss << "}";
+  }
+  ss << "]" << std::endl;
+
+  ss << "}" << std::endl;
+
+  return ss.str();
+}
+
 void GBDT::SaveModelToFile(int num_iteration, const char* filename) const {
   /*! \brief File to write models */
   std::ofstream output_file;
@@ -426,7 +456,11 @@ void GBDT::SaveModelToFile(int num_iteration, const char* filename) const {
     output_file << models_[i]->ToString() << std::endl;
   }
 
-  output_file << std::endl << FeatureImportance() << std::endl;
+  std::vector<std::pair<size_t, std::string>> pairs = FeatureImportance();
+  output_file << std::endl << "feature importances:" << std::endl;
+  for (size_t i = 0; i < pairs.size(); ++i) {
+    output_file << pairs[i].second << "=" << std::to_string(pairs[i].first) << std::endl;
+  }
   output_file.close();
 }
 
@@ -487,7 +521,7 @@ void GBDT::LoadModelFromString(const std::string& model_str) {
   num_init_iteration_ = num_iteration_for_pred_;
 }
 
-std::string GBDT::FeatureImportance() const {
+std::vector<std::pair<size_t, std::string>> GBDT::FeatureImportance() const {
   std::vector<size_t> feature_importances(max_feature_idx_ + 1, 0);
     for (size_t iter = 0; iter < models_.size(); ++iter) {
         for (int split_idx = 0; split_idx < models_[iter]->num_leaves() - 1; ++split_idx) {
@@ -507,13 +541,7 @@ std::string GBDT::FeatureImportance() const {
         const std::pair<size_t, std::string>& rhs) {
       return lhs.first > rhs.first;
     });
-    std::stringstream str_buf;
-    // write to model file
-    str_buf << std::endl << "feature importances:" << std::endl;
-    for (size_t i = 0; i < pairs.size(); ++i) {
-      str_buf << pairs[i].second << "=" << std::to_string(pairs[i].first) << std::endl;
-    }
-    return str_buf.str();
+    return pairs;
 }
 
 std::vector<double> GBDT::PredictRaw(const double* value) const {

src/boosting/gbdt.h

@@ -145,9 +145,16 @@ public:
   std::vector<int> PredictLeafIndex(const double* value) const override;
 
   /*!
-  * \brief save model to file
-  * \param num_iterations Iterations that want to save, -1 means save all
-  * \param filename filename that want to save to
+  * \brief Dump model to json format string
+  * \return Json format string of model
+  */
+  std::string DumpModel() const override;
+
+  /*!
+  * \brief Save model to file
+  * \param num_used_model Number of model that want to save, -1 means save all
+  * \param is_finish Is training finished or not
+  * \param filename Filename that want to save to
   */
   virtual void SaveModelToFile(int num_iterations, const char* filename) const override ;
 
@@ -155,6 +162,7 @@ public:
   * \brief Restore from a serialized string
   */
   void LoadModelFromString(const std::string& model_str) override;
+
   /*!
   * \brief Get max feature index of this model
   * \return Max feature index of this model
@@ -231,7 +239,7 @@ protected:
   * \brief Calculate feature importances
   * \param last_iter Last tree use to calculate
   */
-  std::string FeatureImportance() const;
+  std::vector<std::pair<size_t, std::string>> FeatureImportance() const;
   /*! \brief current iteration */
   int iter_;
   /*! \brief Pointer to training data */

src/c_api.cpp

@@ -139,6 +139,10 @@ public:
     boosting_->SaveModelToFile(num_iteration, filename);
   }
 
+  std::string DumpModel() {
+    return boosting_->DumpModel();
+  }
+
   int GetEvalCounts() const {
     int ret = 0;
     for (const auto& metric : train_metric_) {
@@ -733,6 +737,20 @@ DllExport int LGBM_BoosterSaveModel(BoosterHandle handle,
   API_END();
 }
 
+DllExport int LGBM_BoosterDumpModel(BoosterHandle handle,
+  int buffer_len,
+  int64_t* out_len,
+  char** out_str) {
+  API_BEGIN();
+  Booster* ref_booster = reinterpret_cast<Booster*>(handle);
+  std::string model = ref_booster->DumpModel();
+  *out_len = static_cast<int64_t>(model.size());
+  if (*out_len <= buffer_len) {
+    std::strcpy(*out_str, model.c_str());
+  }
+  API_END();
+}
+
 // ---- start of some help functions
 
 std::function<std::vector<double>(int row_idx)>

src/io/tree.cpp

@@ -125,6 +125,43 @@ std::string Tree::ToString() {
   return ss.str();
 }
 
+std::string Tree::ToJSON() {
+  std::stringstream ss;
+
+  ss << "\"num_leaves\":" << num_leaves_ << "," << std::endl;
+
+  ss << "\"tree_structure\":" << NodeToJSON(0) << std::endl;
+
+  return ss.str();
+}
+
+std::string Tree::NodeToJSON(int index) {
+  std::stringstream ss;
+
+  if (index >= 0) {
+    // non-leaf
+    ss << "{" << std::endl;
+    ss << "\"split_index\":" << index << "," << std::endl;
+    ss << "\"split_feature\":" << split_feature_real_.data()[index] << "," << std::endl;
+    ss << "\"split_gain\":" << split_gain_.data()[index] << "," << std::endl;
+    ss << "\"threshold\":" << threshold_.data()[index] << "," << std::endl;
+    ss << "\"internal_value\":" << internal_value_.data()[index] << "," << std::endl;
+    ss << "\"left_child\":" << NodeToJSON(left_child_.data()[index]) << "," << std::endl;
+    ss << "\"right_child\":" << NodeToJSON(right_child_.data()[index]) << std::endl;
+    ss << "}";
+  } else {
+    // leaf
+    index = ~index;
+    ss << "{" << std::endl;
+    ss << "\"leaf_index\":" << index << "," << std::endl;
+    ss << "\"leaf_parent\":" << leaf_parent_.data()[index] << "," << std::endl;
+    ss << "\"leaf_value\":" << leaf_value_.data()[index] << std::endl;
+    ss << "}";
+  }
+
+  return ss.str();
+}
+
 Tree::Tree(const std::string& str) {
   std::vector<std::string> lines = Common::Split(str.c_str(), '\n');
   std::unordered_map<std::string, std::string> key_vals;

tests/python_package_test/test_basic.py

+# coding: utf-8
 import numpy as np
 from sklearn import datasets, metrics, model_selection
 import lightgbm as lgb
 
-
 X, Y = datasets.make_classification(n_samples=100000, n_features=100)
 x_train, x_test, y_train, y_test = model_selection.train_test_split(X, Y, test_size=0.1)