Gensim word2vec training error on tweets
In newer W2V version it is not enough just to write:

model_name.train(sentences)


You have to write inside word_count or total_examples.

For example, I write:

model_name.train(sentences, total_examples = token_count, epochs = model_name.iter )


where token_count = sum([len(sentence) for sentence in sentences]). And here is how I get sentences:  

sentences = []
for raw_sentence in raw_sentences:

    if len(raw_sentence) &gt; 0:
        sentences.append(sentence_to_wordlist(raw_sentence))


More documentation here.