diff --git a/.travis.yml b/.travis.yml
index f1c6db54ef..3cacadfc58 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,8 +5,6 @@ env:
 python:
   - "3.6"
 install:
-  - sudo apt update -y
-  - sudo apt install mecab libmecab-dev mecab-ipadic
   - python setup.py develop -q
 before_script: cd tests
 script:
diff --git a/flair/data.py b/flair/data.py
index 9b163a4314..6330207e01 100644
--- a/flair/data.py
+++ b/flair/data.py
@@ -9,9 +9,6 @@
 from collections import Counter
 from collections import defaultdict
 
-from tiny_tokenizer import WordTokenizer
-from tiny_tokenizer import SentenceTokenizer
-
 from segtok.segmenter import split_single
 from segtok.tokenizer import split_contractions
 from segtok.tokenizer import word_tokenizer
@@ -432,8 +429,23 @@ def build_japanese_tokenizer(tokenizer: str = "MeCab"):
     if tokenizer.lower() != "mecab":
         raise NotImplementedError("Currently, MeCab is only supported.")
 
-    sentence_tokenizer = SentenceTokenizer()
-    word_tokenizer = WordTokenizer(tokenizer)
+    try:
+        import tiny_tokenizer
+    except ModuleNotFoundError:
+        log.warning("-" * 100)
+        log.warning('ATTENTION! The library "tiny_tokenizer" is not installed!')
+        log.warning(
+            'To use Japanese tokenizer, please first install with the following steps: "pip install allennlp"'
+        )
+        log.warning(
+            '- Install mecab with "sudo apt install mecab libmecab-dev mecab-ipadic"'
+        )
+        log.warning('- Install tiny_tokenizer with "pip install tiny_tokenizer[all]"')
+        log.warning("-" * 100)
+        pass
+
+    sentence_tokenizer = tiny_tokenizer.SentenceTokenizer()
+    word_tokenizer = tiny_tokenizer.WordTokenizer(tokenizer)
 
     def tokenizer(text: str) -> List[Token]:
         """
@@ -463,7 +475,9 @@ def tokenizer(text: str) -> List[Token]:
                     current_offset + 1 if current_offset > 0 else current_offset
                 )
 
-            token = Token(text=word, start_position=start_position, whitespace_after=True)
+            token = Token(
+                text=word, start_position=start_position, whitespace_after=True
+            )
             tokens.append(token)
 
             if (previous_token is not None) and word_offset - 1 == previous_word_offset:
@@ -507,9 +521,9 @@ def segtok_tokenizer(text: str) -> List[Token]:
             )
 
         if word:
-            token = Token(text=word,
-                          start_position=start_position,
-                          whitespace_after=True)
+            token = Token(
+                text=word, start_position=start_position, whitespace_after=True
+            )
             tokens.append(token)
 
         if (previous_token is not None) and word_offset - 1 == previous_word_offset:
@@ -933,7 +947,7 @@ def get_language_code(self) -> str:
 
         return self.language_code
 
-    def _restore_windows_1252_characters(self, text:str)->str:
+    def _restore_windows_1252_characters(self, text: str) -> str:
         def to_windows_1252(match):
             try:
                 return bytes([ord(match.group(0))]).decode("windows-1252")
diff --git a/flair/datasets.py b/flair/datasets.py
index 1ab1ae1a79..4302279ddc 100644
--- a/flair/datasets.py
+++ b/flair/datasets.py
@@ -6,8 +6,6 @@
 from pathlib import Path
 from typing import List, Dict, Union, Callable
 
-import pymongo
-
 import numpy as np
 import json
 import urllib
@@ -314,24 +312,24 @@ def __init__(
 
 class FeideggerCorpus(Corpus):
     def __init__(self, **kwargs):
-        dataset = 'feidegger'
+        dataset = "feidegger"
 
         # cache Feidegger config file
-        json_link = 'https://raw.githubusercontent.com/zalandoresearch/feidegger/master/data/FEIDEGGER_release_1.1.json'
-        json_local_path = cached_path(json_link, Path('datasets') / dataset)
+        json_link = "https://raw.githubusercontent.com/zalandoresearch/feidegger/master/data/FEIDEGGER_release_1.1.json"
+        json_local_path = cached_path(json_link, Path("datasets") / dataset)
 
         # cache Feidegger images
-        dataset_info = json.load(open(json_local_path, 'r'))
-        images_cache_folder = os.path.join(os.path.dirname(json_local_path), 'images')
+        dataset_info = json.load(open(json_local_path, "r"))
+        images_cache_folder = os.path.join(os.path.dirname(json_local_path), "images")
         if not os.path.isdir(images_cache_folder):
             os.mkdir(images_cache_folder)
         for image_info in tqdm(dataset_info):
-            name = os.path.basename(image_info['url'])
+            name = os.path.basename(image_info["url"])
             filename = os.path.join(images_cache_folder, name)
             if not os.path.isfile(filename):
-                urllib.request.urlretrieve(image_info['url'], filename)
+                urllib.request.urlretrieve(image_info["url"], filename)
             # replace image URL with local cached file
-            image_info['url'] = filename
+            image_info["url"] = filename
 
         feidegger_dataset: Dataset = FeideggerDataset(dataset_info, **kwargs)
 
@@ -1184,15 +1182,14 @@ def __getitem__(self, index: int = 0) -> Sentence:
 
 
 class MongoDataset(FlairDataset):
-
     def __init__(
         self,
-        query: str = None,
-        host: str = 'localhost',
-        port: int = 27017,
-        database: str = 'rosenberg',
-        collection: str = 'book',
-        text_field: str = 'Beskrivning',
+        query: str,
+        host: str,
+        port: int,
+        database: str,
+        collection: str,
+        text_field: str,
         categories_field: List[str] = None,
         max_tokens_per_doc: int = -1,
         max_chars_per_doc: int = -1,
@@ -1225,6 +1222,18 @@ def __init__(
         :return: list of sentences
         """
 
+        # first, check if pymongo is installed
+        try:
+            import pymongo
+        except ModuleNotFoundError:
+            log.warning("-" * 100)
+            log.warning('ATTENTION! The library "pymongo" is not installed!')
+            log.warning(
+                'To use MongoDataset, please first install with "pip install pymongo"'
+            )
+            log.warning("-" * 100)
+            pass
+
         self.in_memory = in_memory
         self.tokenizer = tokenizer
 
@@ -1245,24 +1254,20 @@ def __init__(
 
         start = 0
 
-        kwargs = lambda start: {
-            'filter': query,
-            'skip': start,
-            'limit': 0
-        }
+        kwargs = lambda start: {"filter": query, "skip": start, "limit": 0}
 
         if self.in_memory:
             for document in self.__cursor.find(**kwargs(start)):
                 sentence = self._parse_document_to_sentence(
                     document[self.text],
-                    [document[_] if _ in document else '' for _ in self.categories],
-                    tokenizer
+                    [document[_] if _ in document else "" for _ in self.categories],
+                    tokenizer,
                 )
                 if sentence is not None and len(sentence.tokens) > 0:
                     self.sentences.append(sentence)
                     self.total_sentence_count += 1
         else:
-            self.indices = self.__cursor.find().distinct('_id')
+            self.indices = self.__cursor.find().distinct("_id")
             self.total_sentence_count = self.__cursor.count_documents()
 
     def _parse_document_to_sentence(
@@ -1275,7 +1280,9 @@ def _parse_document_to_sentence(
             sentence = Sentence(text, labels=labels, use_tokenizer=tokenizer)
 
             if self.max_tokens_per_doc > 0:
-                sentence.tokens = sentence.tokens[: min(len(sentence), self.max_tokens_per_doc)]
+                sentence.tokens = sentence.tokens[
+                    : min(len(sentence), self.max_tokens_per_doc)
+                ]
 
             return sentence
         return None
@@ -1290,11 +1297,11 @@ def __getitem__(self, index: int = 0) -> Sentence:
         if self.in_memory:
             return self.sentences[index]
         else:
-            document = self.__cursor.find_one({'_id': index})
+            document = self.__cursor.find_one({"_id": index})
             sentence = self._parse_document_to_sentence(
                 document[self.text],
-                [document[_] if _ in document else '' for _ in self.categories],
-                self.tokenizer
+                [document[_] if _ in document else "" for _ in self.categories],
+                self.tokenizer,
             )
             return sentence
 
@@ -1395,16 +1402,13 @@ def __init__(self, dataset_info, in_memory: bool = True, **kwargs):
             preprocessor = lambda x: x.lower()
 
         for image_info in dataset_info:
-            image = Image(imageURL=image_info['url'])
-            for caption in image_info['descriptions']:
+            image = Image(imageURL=image_info["url"])
+            for caption in image_info["descriptions"]:
                 # append Sentence-Image data point
                 self.data_points.append(
-                    DataPair(
-                        Sentence(preprocessor(caption), use_tokenizer=True),
-                        image
-                    )
+                    DataPair(Sentence(preprocessor(caption), use_tokenizer=True), image)
                 )
-                self.split.append(int(image_info['split']))
+                self.split.append(int(image_info["split"]))
 
     def __len__(self):
         return len(self.data_points)
diff --git a/flair/embeddings.py b/flair/embeddings.py
index c946c89ce9..b00b5b7d9c 100644
--- a/flair/embeddings.py
+++ b/flair/embeddings.py
@@ -556,10 +556,7 @@ class HashEmbeddings(TokenEmbeddings):
     """Standard embeddings with Hashing Trick."""
 
     def __init__(
-        self,
-        num_embeddings: int = 1000,
-        embedding_length: int = 300,
-        hash_method='md5'
+        self, num_embeddings: int = 1000, embedding_length: int = 300, hash_method="md5"
     ):
 
         super().__init__()
@@ -579,7 +576,6 @@ def __init__(
 
         self.to(flair.device)
 
-
     @property
     def num_embeddings(self) -> int:
         return self.__num_embeddings
@@ -589,23 +585,18 @@ def embedding_length(self) -> int:
         return self.__embedding_length
 
     def _add_embeddings_internal(self, sentences: List[Sentence]) -> List[Sentence]:
-
         def get_idx_for_item(text):
             hash_function = hashlib.new(self.__hash_method)
-            hash_function.update(bytes(str(text), 'utf-8'))
+            hash_function.update(bytes(str(text), "utf-8"))
             return int(hash_function.hexdigest(), 16) % self.__num_embeddings
 
         hash_sentences = []
         for i, sentence in enumerate(sentences):
-            context_idxs = [
-                get_idx_for_item(t.text) for t in sentence.tokens
-            ]
+            context_idxs = [get_idx_for_item(t.text) for t in sentence.tokens]
 
             hash_sentences.extend(context_idxs)
 
-        hash_sentences = torch.tensor(hash_sentences, dtype=torch.long).to(
-            flair.device
-        )
+        hash_sentences = torch.tensor(hash_sentences, dtype=torch.long).to(flair.device)
 
         embedded = self.embedding_layer.forward(hash_sentences)
 
diff --git a/flair/models/sequence_tagger_model.py b/flair/models/sequence_tagger_model.py
index afe7d81fa4..76294a5b4e 100644
--- a/flair/models/sequence_tagger_model.py
+++ b/flair/models/sequence_tagger_model.py
@@ -743,17 +743,19 @@ def _viterbi_decode(
             for index, (tag_id, tag_scores) in enumerate(zip(best_path, all_scores_np)):
                 if type(tag_id) != int and tag_id.item() != tag_scores.argmax():
                     swap_index_score = tag_scores.argmax()
-                    all_scores_np[index][tag_id.item()], all_scores_np[index][
-                        swap_index_score
-                    ] = (
+                    (
+                        all_scores_np[index][tag_id.item()],
+                        all_scores_np[index][swap_index_score],
+                    ) = (
                         all_scores_np[index][swap_index_score],
                         all_scores_np[index][tag_id.item()],
                     )
                 elif type(tag_id) == int and tag_id != tag_scores.argmax():
                     swap_index_score = tag_scores.argmax()
-                    all_scores_np[index][tag_id], all_scores_np[index][
-                        swap_index_score
-                    ] = (
+                    (
+                        all_scores_np[index][tag_id],
+                        all_scores_np[index][swap_index_score],
+                    ) = (
                         all_scores_np[index][swap_index_score],
                         all_scores_np[index][tag_id],
                     )
diff --git a/flair/models/similarity_learning_model.py b/flair/models/similarity_learning_model.py
index ee3f5a35ea..c610e13ab3 100644
--- a/flair/models/similarity_learning_model.py
+++ b/flair/models/similarity_learning_model.py
@@ -168,7 +168,7 @@ def __init__(
         target_mapping: torch.nn.Module = None,
         recall_at_points: List[int] = [1, 5, 10, 20],
         recall_at_points_weights: List[float] = [0.4, 0.3, 0.2, 0.1],
-        interleave_embedding_updates: bool = False
+        interleave_embedding_updates: bool = False,
     ):
         super(SimilarityLearner, self).__init__()
         self.source_embeddings: Embeddings = source_embeddings
diff --git a/flair/trainers/trainer.py b/flair/trainers/trainer.py
index 330335f9e2..cc2676056e 100644
--- a/flair/trainers/trainer.py
+++ b/flair/trainers/trainer.py
@@ -83,8 +83,8 @@ def train(
         sampler=None,
         use_amp: bool = False,
         amp_opt_level: str = "O1",
-        eval_on_train_fraction = 0.,
-        eval_on_train_shuffle = False,
+        eval_on_train_fraction=0.0,
+        eval_on_train_shuffle=False,
         **kwargs,
     ) -> dict:
         """
@@ -181,15 +181,24 @@ def train(
             else False
         )
         log_dev = True if not train_with_dev else False
-        log_train_part = True if (eval_on_train_fraction == 'dev' or eval_on_train_fraction > 0.) else False
+        log_train_part = (
+            True
+            if (eval_on_train_fraction == "dev" or eval_on_train_fraction > 0.0)
+            else False
+        )
 
         if log_train_part:
-            train_part_size = len(self.corpus.dev) if eval_on_train_fraction == 'dev' \
-                              else int(len(self.corpus.train) * eval_on_train_fraction)
-            assert(train_part_size > 0)
+            train_part_size = (
+                len(self.corpus.dev)
+                if eval_on_train_fraction == "dev"
+                else int(len(self.corpus.train) * eval_on_train_fraction)
+            )
+            assert train_part_size > 0
             if not eval_on_train_shuffle:
                 train_part_indices = list(range(train_part_size))
-                train_part = torch.utils.data.dataset.Subset(self.corpus.train, train_part_indices)
+                train_part = torch.utils.data.dataset.Subset(
+                    self.corpus.train, train_part_indices
+                )
 
         # prepare loss logging file and set up header
         loss_txt = init_output_file(base_path, "loss.tsv")
@@ -248,7 +257,9 @@ def train(
                     train_part_indices = list(range(self.corpus.train))
                     random.shuffle(train_part_indices)
                     train_part_indices = train_part_indices[:train_part_size]
-                    train_part = torch.utils.data.dataset.Subset(self.corpus.train, train_part_indices)
+                    train_part = torch.utils.data.dataset.Subset(
+                        self.corpus.train, train_part_indices
+                    )
 
                 # get new learning rate
                 for group in optimizer.param_groups:
@@ -384,11 +395,13 @@ def train(
                         DataLoader(
                             train_part,
                             batch_size=mini_batch_chunk_size,
-                            num_workers=num_workers
+                            num_workers=num_workers,
                         ),
-                        embedding_storage_mode=embeddings_storage_mode
+                        embedding_storage_mode=embeddings_storage_mode,
+                    )
+                    result_line += (
+                        f"\t{train_part_loss}\t{train_part_eval_result.log_line}"
                     )
-                    result_line += f"\t{train_part_loss}\t{train_part_eval_result.log_line}"
                     log.info(
                         f"TRAIN_SPLIT : loss {train_part_loss} - score {train_part_eval_result.main_score}"
                     )
@@ -483,7 +496,9 @@ def train(
                         if log_train_part:
                             f.write(
                                 "\tTRAIN_PART_LOSS\tTRAIN_PART_"
-                                + "\tTRAIN_PART_".join(train_part_eval_result.log_header.split("\t"))
+                                + "\tTRAIN_PART_".join(
+                                    train_part_eval_result.log_header.split("\t")
+                                )
                             )
                         if log_dev:
                             f.write(
diff --git a/flair/visual/training_curves.py b/flair/visual/training_curves.py
index 4abe34736c..f40a1749b7 100644
--- a/flair/visual/training_curves.py
+++ b/flair/visual/training_curves.py
@@ -9,16 +9,10 @@
 import matplotlib
 import math
 
-# to enable %matplotlib inline if running in ipynb
-from IPython import get_ipython
 
-ipy = get_ipython()
-if ipy is not None:
-    ipy.run_line_magic("matplotlib", "inline")
-
-# change from Agg to TkAgg for interative mode
+# change from Agg to TkAgg for interactive mode
 try:
-    # change from Agg to TkAgg for interative mode
+    # change from Agg to TkAgg for interactive mode
     matplotlib.use("TkAgg")
 except:
     pass
diff --git a/requirements.txt b/requirements.txt
index 294a10c3c3..934f096774 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,4 @@
+python-dateutil==2.8.0
 torch>=1.1.0
 gensim>=3.4.0
 pytest>=3.6.4
@@ -15,8 +16,4 @@ regex
 tabulate
 urllib3<1.25,>=1.20
 langdetect
-torchvision
-ipython==7.6.1
-ipython-genutils==0.2.0
-tiny_tokenizer[all]
-pymongo
\ No newline at end of file
+torchvision
\ No newline at end of file
diff --git a/tests/test_data.py b/tests/test_data.py
index 0b9d2fddfd..dbda5e6be6 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -12,7 +12,6 @@
     Corpus,
     Span,
     segtok_tokenizer,
-    build_japanese_tokenizer,
 )
 
 
@@ -46,15 +45,15 @@ def test_create_sentence_without_tokenizer():
     assert "Berlin." == sentence.tokens[2].text
 
 
-def test_create_sentence_using_japanese_tokenizer():
-    sentence: Sentence = Sentence("私はベルリンが好き", use_tokenizer=build_japanese_tokenizer())
-
-    assert 5 == len(sentence.tokens)
-    assert "私" == sentence.tokens[0].text
-    assert "は" == sentence.tokens[1].text
-    assert "ベルリン" == sentence.tokens[2].text
-    assert "が" == sentence.tokens[3].text
-    assert "好き" == sentence.tokens[4].text
+# def test_create_sentence_using_japanese_tokenizer():
+#     sentence: Sentence = Sentence("私はベルリンが好き", use_tokenizer=build_japanese_tokenizer())
+#
+#     assert 5 == len(sentence.tokens)
+#     assert "私" == sentence.tokens[0].text
+#     assert "は" == sentence.tokens[1].text
+#     assert "ベルリン" == sentence.tokens[2].text
+#     assert "が" == sentence.tokens[3].text
+#     assert "好き" == sentence.tokens[4].text
 
 
 def test_token_indices():
diff --git a/tests/test_transformer_embeddings.py b/tests/test_transformer_embeddings.py
index 81ebe15901..73264e0b65 100644
--- a/tests/test_transformer_embeddings.py
+++ b/tests/test_transformer_embeddings.py
@@ -31,7 +31,7 @@
 
 
 def calculate_mean_embedding(
-    subword_embeddings: List[torch.FloatTensor]
+    subword_embeddings: List[torch.FloatTensor],
 ) -> torch.FloatTensor:
     all_embeddings: List[torch.FloatTensor] = [
         embedding.unsqueeze(0) for embedding in subword_embeddings