fine_tune.py

from flair.data import Corpus
from flair.datasets import ColumnCorpus

columns = {0: 'text', 1: 'pos', 3: 'ner'}

# this is the folder in which train, test and dev files reside
data_folder = 'data/ner/bc5dr'

# init a corpus using column format, data folder and the names of the train, dev and test files
corpus: Corpus = ColumnCorpus(data_folder, columns,
                              train_file='train.txt',
                              test_file='test.txt',
                              dev_file='dev.txt')
tag_type = 'ner'
tag_dictionary = corpus.make_tag_dictionary(tag_type=tag_type)

from flair.embeddings import TokenEmbeddings, WordEmbeddings, StackedEmbeddings, PooledFlairEmbeddings, ELMoEmbeddings
from typing import List
embedding_types: List[TokenEmbeddings] = [
    PooledFlairEmbeddings('pubmed-forward'),
    PooledFlairEmbeddings('pubmed-backward'),
    ELMoEmbeddings('pubmed'),
]
embeddings: StackedEmbeddings = StackedEmbeddings(embeddings=embedding_types)

from flair.models import SequenceTagger

tagger: SequenceTagger = SequenceTagger(hidden_size=256,
                                        embeddings=embeddings,
                                        tag_dictionary=tag_dictionary,
                                        tag_type=tag_type,
                                        use_crf=True)
#  initialize trainer
from flair.trainers import ModelTrainer

trainer: ModelTrainer = ModelTrainer(tagger, corpus)

#  start training
trainer.train('ner/models/v1',
              learning_rate=0.1,
              mini_batch_size=32,
              max_epochs=150)