Keras Text Preprocessing - Saving Tokenizer object to file for scoring - machine-learning

Question

I've trained a sentiment classifier model using Keras library by following the below steps(broadly).
Convert Text corpus into sequences using Tokenizer object/class
Build a model using the model.fit() method
Evaluate this model
Now for scoring using this model, I was able to save the model to a file and load from a file. However I've not found a way to save the Tokenizer object to file. Without this I'll have to process the corpus every time I need to score even a single sentence. Is there a way around this?

Answer 1

The most common way is to use either pickle or joblib. Here you have an example on how to use pickle in order to save Tokenizer:
import pickle
# saving
with open('tokenizer.pickle', 'wb') as handle:
pickle.dump(tokenizer, handle, protocol=pickle.HIGHEST_PROTOCOL)
# loading
with open('tokenizer.pickle', 'rb') as handle:
tokenizer = pickle.load(handle)

Answer 2

Tokenizer class has a function to save date into JSON format:
tokenizer_json = tokenizer.to_json()
with io.open('tokenizer.json', 'w', encoding='utf-8') as f:
f.write(json.dumps(tokenizer_json, ensure_ascii=False))
The data can be loaded using tokenizer_from_json function from keras_preprocessing.text:
with open('tokenizer.json') as f:
data = json.load(f)
tokenizer = tokenizer_from_json(data)

Answer 3

The accepted answer clearly demonstrates how to save the tokenizer. The following is a comment on the problem of (generally) scoring after fitting or saving. Suppose that a list texts is comprised of two lists Train_text and Test_text, where the set of tokens in Test_text is a subset of the set of tokens in Train_text (an optimistic assumption). Then fit_on_texts(Train_text) gives different results for texts_to_sequences(Test_text) as compared with first calling fit_on_texts(texts) and then text_to_sequences(Test_text).
Concrete Example:
from keras.preprocessing.text import Tokenizer
docs = ["A heart that",
"full up like",
"a landfill",
"no surprises",
"and no alarms"
"a job that slowly"
"Bruises that",
"You look so",
"tired happy",
"no alarms",
"and no surprises"]
docs_train = docs[:7]
docs_test = docs[7:]
# EXPERIMENT 1: FIT TOKENIZER ONLY ON TRAIN
T_1 = Tokenizer()
T_1.fit_on_texts(docs_train) # only train set
encoded_train_1 = T_1.texts_to_sequences(docs_train)
encoded_test_1 = T_1.texts_to_sequences(docs_test)
print("result for test 1:\n%s" %(encoded_test_1,))
# EXPERIMENT 2: FIT TOKENIZER ON BOTH TRAIN + TEST
T_2 = Tokenizer()
T_2.fit_on_texts(docs) # both train and test set
encoded_train_2 = T_2.texts_to_sequences(docs_train)
encoded_test_2 = T_2.texts_to_sequences(docs_test)
print("result for test 2:\n%s" %(encoded_test_2,))
Results:
result for test 1:
[[3], [10, 3, 9]]
result for test 2:
[[1, 19], [5, 1, 4]]
Of course, if the above optimistic assumption is not satisfied and the set of tokens in Test_text is disjoint from that of Train_test, then test 1 results in a list of empty brackets [].

Answer 4

I've created the issue https://github.com/keras-team/keras/issues/9289 in the keras Repo. Until the API is changed, the issue has a link to a gist that has code to demonstrate how to save and restore a tokenizer without having the original documents the tokenizer was fit on. I prefer to store all my model information in a JSON file (because reasons, but mainly mixed JS/Python environment), and this will allow for that, even with sort_keys=True

Answer 5

I found the following snippet provided at following link by #thusv89.
Save objects:
import pickle
with open('data_objects.pickle', 'wb') as handle:
pickle.dump(
{'input_tensor': input_tensor,
'target_tensor': target_tensor,
'inp_lang': inp_lang,
'targ_lang': targ_lang,
}, handle, protocol=pickle.HIGHEST_PROTOCOL)
Load objects:
with open("dataset_fr_en.pickle", 'rb') as f:
data = pickle.load(f)
input_tensor = data['input_tensor']
target_tensor = data['target_tensor']
inp_lang = data['inp_lang']
targ_lang = data['targ_lang']

Answer 6

Quite easy, because Tokenizer class has provided two funtions for save and load:
save —— Tokenizer.to_json()
load —— keras.preprocessing.text.tokenizer_from_json
In to_json() method，it call "get_config" method which handle this:
json_word_counts = json.dumps(self.word_counts)
json_word_docs = json.dumps(self.word_docs)
json_index_docs = json.dumps(self.index_docs)
json_word_index = json.dumps(self.word_index)
json_index_word = json.dumps(self.index_word)
return {
'num_words': self.num_words,
'filters': self.filters,
'lower': self.lower,
'split': self.split,
'char_level': self.char_level,
'oov_token': self.oov_token,
'document_count': self.document_count,
'word_counts': json_word_counts,
'word_docs': json_word_docs,
'index_docs': json_index_docs,
'index_word': json_index_word,
'word_index': json_word_index
}