Re-design "*2vec" implementations

gensim/__init__.py

@@ -3,7 +3,7 @@
 similarities within a corpus of documents.
 """
 
-from gensim import parsing, matutils, interfaces, corpora, models, similarities, summarization, utils  # noqa:F401
+from gensim import parsing, matutils, interfaces, corpora, models, similarities, summarization, utils, callbacks  # noqa:F401
 import logging
 
 __version__ = '3.2.0'

gensim/callbacks.py

@@ -0,0 +1,49 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""
+Abstract base class to build callbacks. Callbacks are used to apply custom functions over the model
+at specific points during training (epoch start, batch end etc.). To implement a Callback, subclass
+:class: ~gensim.callbacks.Callback, look at the example below which creates a callback to save a training model
+after each epoch:
+
+>>> from gensim.test.utils import common_texts as sentences
+>>> from gensim.callbacks import Callback
+>>> from gensim.models import word2vec
+>>> class ModelEpochSaver(Callback):  # Callback to save model after every epoch
+>>>     def __init__(self, path_prefix):
+>>>         self.path_prefix = path_prefix
+>>>     def on_epoch_end(self, model):
+>>>         model.save('{}_epoch{}'.format(self.path_prefix, self.cur_epoch))
+>>>         self.cur_epoch += 1
+>>>     def on_train_begin(self, model):
+>>>         self.cur_epoch = 0
+>>> epoch_saver = ModelEpochSaver('axax')
+>>> model = word2vec.Word2Vec(sentences, iter=5, size=10, min_count=0, seed=42, callbacks=[epoch_saver])
+
+"""
+
+
+class Callback(object):
+    """Abstract base class used to build new callbacks."""
+
+    def __init__(self):
+        pass
+
+    def on_epoch_begin(self, model):
+        pass
+
+    def on_epoch_end(self, model):
+        pass
+
+    def on_batch_begin(self, model):
+        pass
+
+    def on_batch_end(self, model):
+        pass
+
+    def on_train_begin(self, model):
+        pass
+
+    def on_train_end(self, model):
+        pass

gensim/models/__init__.py

@@ -13,7 +13,7 @@
 from .logentropy_model import LogEntropyModel  # noqa:F401
 from .word2vec import Word2Vec  # noqa:F401
 from .doc2vec import Doc2Vec  # noqa:F401
-from .keyedvectors import KeyedVectors  # noqa:F401
+from .word2vec import Word2VecKeyedVectors as KeyedVectors  # noqa:F401
 from .ldamulticore import LdaMulticore  # noqa:F401
 from .phrases import Phrases  # noqa:F401
 from .normmodel import NormModel  # noqa:F401