diff --git a/docs/_src/api/api/document_store.md b/docs/_src/api/api/document_store.md
index 3389b808d..1ba470b4e 100644
--- a/docs/_src/api/api/document_store.md
+++ b/docs/_src/api/api/document_store.md
@@ -295,7 +295,7 @@ that are most relevant to the query as defined by the BM25 algorithm.
 #### query\_by\_embedding
 
 ```python
- | query_by_embedding(query_emb: np.array, filters: Optional[Dict[str, List[str]]] = None, top_k: int = 10, index: Optional[str] = None, return_embedding: Optional[bool] = None) -> List[Document]
+ | query_by_embedding(query_emb: np.ndarray, filters: Optional[Dict[str, List[str]]] = None, top_k: int = 10, index: Optional[str] = None, return_embedding: Optional[bool] = None) -> List[Document]
 ```
 
 Find the document that is most similar to the provided `query_emb` by using a vector similarity metric.
@@ -453,7 +453,7 @@ Fetch documents by specifying a list of text id strings
 #### query\_by\_embedding
 
 ```python
- | query_by_embedding(query_emb: List[float], filters: Optional[Dict[str, List[str]]] = None, top_k: int = 10, index: Optional[str] = None, return_embedding: Optional[bool] = None) -> List[Document]
+ | query_by_embedding(query_emb: np.ndarray, filters: Optional[Dict[str, List[str]]] = None, top_k: int = 10, index: Optional[str] = None, return_embedding: Optional[bool] = None) -> List[Document]
 ```
 
 Find the document that is most similar to the provided `query_emb` by using a vector similarity metric.
@@ -863,7 +863,7 @@ Example: {"name": ["some", "more"], "category": ["only_one"]}
 #### train\_index
 
 ```python
- | train_index(documents: Optional[Union[List[dict], List[Document]]], embeddings: Optional[np.array] = None)
+ | train_index(documents: Optional[Union[List[dict], List[Document]]], embeddings: Optional[np.ndarray] = None)
 ```
 
 Some FAISS indices (e.g. IVF) require initial "training" on a sample of vectors before you can add your final vectors.
@@ -892,7 +892,7 @@ Delete all documents from the document store.
 #### query\_by\_embedding
 
 ```python
- | query_by_embedding(query_emb: np.array, filters: Optional[dict] = None, top_k: int = 10, index: Optional[str] = None, return_embedding: Optional[bool] = None) -> List[Document]
+ | query_by_embedding(query_emb: np.ndarray, filters: Optional[dict] = None, top_k: int = 10, index: Optional[str] = None, return_embedding: Optional[bool] = None) -> List[Document]
 ```
 
 Find the document that is most similar to the provided `query_emb` by using a vector similarity metric.
diff --git a/docs/_src/api/api/retriever.md b/docs/_src/api/api/retriever.md
index d943dc69f..0d86faa7e 100644
--- a/docs/_src/api/api/retriever.md
+++ b/docs/_src/api/api/retriever.md
@@ -286,7 +286,7 @@ that are most relevant to the query.
 #### embed\_queries
 
 ```python
- | embed_queries(texts: List[str]) -> List[np.array]
+ | embed_queries(texts: List[str]) -> List[np.ndarray]
 ```
 
 Create embeddings for a list of queries using the query encoder
@@ -303,7 +303,7 @@ Embeddings, one per input queries
 #### embed\_passages
 
 ```python
- | embed_passages(docs: List[Document]) -> List[np.array]
+ | embed_passages(docs: List[Document]) -> List[np.ndarray]
 ```
 
 Create embeddings for a list of passages using the passage encoder
@@ -434,7 +434,7 @@ that are most relevant to the query.
 #### embed
 
 ```python
- | embed(texts: Union[List[str], str]) -> List[np.array]
+ | embed(texts: Union[List[str], str]) -> List[np.ndarray]
 ```
 
 Create embeddings for each text in a list of texts using the retrievers model (`self.embedding_model`)
@@ -451,7 +451,7 @@ List of embeddings (one per input text). Each embedding is a list of floats.
 #### embed\_queries
 
 ```python
- | embed_queries(texts: List[str]) -> List[np.array]
+ | embed_queries(texts: List[str]) -> List[np.ndarray]
 ```
 
 Create embeddings for a list of queries. For this Retriever type: The same as calling .embed()
@@ -468,7 +468,7 @@ Embeddings, one per input queries
 #### embed\_passages
 
 ```python
- | embed_passages(docs: List[Document]) -> List[np.array]
+ | embed_passages(docs: List[Document]) -> List[np.ndarray]
 ```
 
 Create embeddings for a list of passages. For this Retriever type: The same as calling .embed()
diff --git a/haystack/document_store/base.py b/haystack/document_store/base.py
index 58bbc7440..281c47247 100644
--- a/haystack/document_store/base.py
+++ b/haystack/document_store/base.py
@@ -1,11 +1,13 @@
 import logging
 from abc import abstractmethod, ABC
 from pathlib import Path
-from typing import Any, Optional, Dict, List, Union
-from haystack import Document, Label, MultiLabel
-from haystack.preprocessor.utils import eval_data_from_json, eval_data_from_jsonl, squad_json_to_jsonl
-from haystack.preprocessor.preprocessor import PreProcessor
+from typing import Optional, Dict, List, Union
 
+import numpy as np
+
+from haystack import Document, Label, MultiLabel
+from haystack.preprocessor.preprocessor import PreProcessor
+from haystack.preprocessor.utils import eval_data_from_json, eval_data_from_jsonl, squad_json_to_jsonl
 
 logger = logging.getLogger(__name__)
 
@@ -64,7 +66,7 @@ class BaseDocumentStore(ABC):
         all_labels = self.get_all_labels(index=index, filters=filters)
 
         # Collect all answers to a question in a dict
-        question_ans_dict = {} # type: ignore
+        question_ans_dict: dict = {}
         for l in all_labels:
             # only aggregate labels with correct answers, as only those can be currently used in evaluation
             if not l.is_correct_answer:
@@ -125,7 +127,7 @@ class BaseDocumentStore(ABC):
 
     @abstractmethod
     def query_by_embedding(self,
-                           query_emb: List[float],
+                           query_emb: np.ndarray,
                            filters: Optional[Optional[Dict[str, List[str]]]] = None,
                            top_k: int = 10,
                            index: Optional[str] = None,
diff --git a/haystack/document_store/elasticsearch.py b/haystack/document_store/elasticsearch.py
index 6c6649f4e..5049446b6 100644
--- a/haystack/document_store/elasticsearch.py
+++ b/haystack/document_store/elasticsearch.py
@@ -568,7 +568,7 @@ class ElasticsearchDocumentStore(BaseDocumentStore):
         return documents
 
     def query_by_embedding(self,
-                           query_emb: np.array,
+                           query_emb: np.ndarray,
                            filters: Optional[Dict[str, List[str]]] = None,
                            top_k: int = 10,
                            index: Optional[str] = None,
@@ -631,7 +631,7 @@ class ElasticsearchDocumentStore(BaseDocumentStore):
             ]
             return documents
 
-    def _get_vector_similarity_query(self, query_emb: np.array, top_k: int):
+    def _get_vector_similarity_query(self, query_emb: np.ndarray, top_k: int):
         """
         Generate Elasticsearch query for vector similarity.
         """
@@ -849,7 +849,7 @@ class OpenDistroElasticsearchDocumentStore(ElasticsearchDocumentStore):
             if not self.client.indices.exists(index=index_name):
                 raise e
 
-    def _get_vector_similarity_query(self, query_emb: np.array, top_k: int):
+    def _get_vector_similarity_query(self, query_emb: np.ndarray, top_k: int):
         """
         Generate Elasticsearch query for vector similarity.
         """
diff --git a/haystack/document_store/faiss.py b/haystack/document_store/faiss.py
index d0df99624..cfa04cad0 100644
--- a/haystack/document_store/faiss.py
+++ b/haystack/document_store/faiss.py
@@ -142,8 +142,8 @@ class FAISSDocumentStore(SQLDocumentStore):
         for i in range(0, len(document_objects), batch_size):
             if add_vectors:
                 embeddings = [doc.embedding for doc in document_objects[i: i + batch_size]]
-                embeddings = np.array(embeddings, dtype="float32")
-                self.faiss_index.add(embeddings)
+                embeddings_to_index = np.array(embeddings, dtype="float32")
+                self.faiss_index.add(embeddings_to_index)
 
             docs_to_write_in_sql = []
             for doc in document_objects[i: i + batch_size]:
@@ -259,7 +259,9 @@ class FAISSDocumentStore(SQLDocumentStore):
                     doc.embedding = self.faiss_index.reconstruct(int(doc.meta["vector_id"]))
         return documents
 
-    def train_index(self, documents: Optional[Union[List[dict], List[Document]]], embeddings: Optional[np.array] = None):
+    def train_index(
+            self, documents: Optional[Union[List[dict], List[Document]]], embeddings: Optional[np.ndarray] = None
+    ):
         """
         Some FAISS indices (e.g. IVF) require initial "training" on a sample of vectors before you can add your final vectors.
         The train vectors should come from the same distribution as your final ones.
@@ -274,9 +276,11 @@ class FAISSDocumentStore(SQLDocumentStore):
             raise ValueError("Either pass `documents` or `embeddings`. You passed both.")
         if documents:
             document_objects = [Document.from_dict(d) if isinstance(d, dict) else d for d in documents]
-            embeddings = [doc.embedding for doc in document_objects]
-            embeddings = np.array(embeddings, dtype="float32")
-        self.faiss_index.train(embeddings)
+            doc_embeddings = [doc.embedding for doc in document_objects]
+            embeddings_for_train = np.array(doc_embeddings, dtype="float32")
+            self.faiss_index.train(embeddings_for_train)
+        if embeddings:
+            self.faiss_index.train(embeddings)
 
     def delete_all_documents(self, index: Optional[str] = None, filters: Optional[Dict[str, List[str]]] = None):
         """
@@ -287,7 +291,7 @@ class FAISSDocumentStore(SQLDocumentStore):
         super().delete_all_documents(index=index, filters=filters)
 
     def query_by_embedding(self,
-                           query_emb: np.array,
+                           query_emb: np.ndarray,
                            filters: Optional[dict] = None,
                            top_k: int = 10,
                            index: Optional[str] = None,
diff --git a/haystack/document_store/memory.py b/haystack/document_store/memory.py
index bb4082bb9..e6eb780d0 100644
--- a/haystack/document_store/memory.py
+++ b/haystack/document_store/memory.py
@@ -1,15 +1,15 @@
+import logging
+from collections import defaultdict
 from copy import deepcopy
 from typing import Dict, List, Optional, Union, Generator
 from uuid import uuid4
-from collections import defaultdict
-
-from haystack.document_store.base import BaseDocumentStore
-from haystack import Document, Label
-from haystack.retriever.base import BaseRetriever
 
+import numpy as np
 from scipy.spatial.distance import cosine
 
-import logging
+from haystack import Document, Label
+from haystack.document_store.base import BaseDocumentStore
+from haystack.retriever.base import BaseRetriever
 
 logger = logging.getLogger(__name__)
 
@@ -94,7 +94,7 @@ class InMemoryDocumentStore(BaseDocumentStore):
         return documents
 
     def query_by_embedding(self,
-                           query_emb: List[float],
+                           query_emb: np.ndarray,
                            filters: Optional[Dict[str, List[str]]] = None,
                            top_k: int = 10,
                            index: Optional[str] = None,
diff --git a/haystack/document_store/milvus.py b/haystack/document_store/milvus.py
index 28332ed0a..4d79d50d0 100644
--- a/haystack/document_store/milvus.py
+++ b/haystack/document_store/milvus.py
@@ -258,7 +258,7 @@ class MilvusDocumentStore(SQLDocumentStore):
         self.milvus_server.compact(collection_name=index)
 
     def query_by_embedding(self,
-                           query_emb: np.array,
+                           query_emb: np.ndarray,
                            filters: Optional[dict] = None,
                            top_k: int = 10,
                            index: Optional[str] = None,
@@ -458,7 +458,7 @@ class MilvusDocumentStore(SQLDocumentStore):
             if status.code != Status.SUCCESS:
                 raise RuntimeError("E existing vector ids deletion failed: {status}")
 
-    def get_all_vectors(self, index=None) -> List[np.array]:
+    def get_all_vectors(self, index: Optional[str] = None) -> List[np.ndarray]:
         """
         Helper function to dump all vectors stored in Milvus server.
 
diff --git a/haystack/document_store/sql.py b/haystack/document_store/sql.py
index e0aa85b25..3a2278fe6 100644
--- a/haystack/document_store/sql.py
+++ b/haystack/document_store/sql.py
@@ -3,6 +3,7 @@ import logging
 from typing import Any, Dict, Union, List, Optional, Generator
 from uuid import uuid4
 
+import numpy as np
 from sqlalchemy import and_, func, create_engine, Column, Integer, String, DateTime, ForeignKey, Boolean, Text, text
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import relationship, sessionmaker
@@ -136,7 +137,7 @@ class SQLDocumentStore(BaseDocumentStore):
             for row in query.all():
                 documents.append(self._convert_sql_row_to_document(row))
 
-        sorted_documents = sorted(documents, key=lambda doc: vector_ids.index(doc.meta["vector_id"]))  # type: ignore
+        sorted_documents = sorted(documents, key=lambda doc: vector_ids.index(doc.meta["vector_id"]))
         return sorted_documents
 
     def get_all_documents(
@@ -196,7 +197,7 @@ class SQLDocumentStore(BaseDocumentStore):
             documents_map[row.id] = Document(
                 id=row.id,
                 text=row.text,
-                meta=None if row.vector_id is None else {"vector_id": row.vector_id}  # type: ignore
+                meta=None if row.vector_id is None else {"vector_id": row.vector_id}
             )
             if i % batch_size == 0:
                 documents_map = self._get_documents_meta(documents_map)
@@ -215,7 +216,7 @@ class SQLDocumentStore(BaseDocumentStore):
         ).filter(MetaORM.document_id.in_(doc_ids))
 
         for row in meta_query.all():
-            documents_map[row.document_id].meta[row.name] = row.value  # type: ignore
+            documents_map[row.document_id].meta[row.name] = row.value
         return documents_map
 
     def get_all_labels(self, index=None, filters: Optional[dict] = None):
@@ -389,7 +390,7 @@ class SQLDocumentStore(BaseDocumentStore):
         return label
 
     def query_by_embedding(self,
-                           query_emb: List[float],
+                           query_emb: np.ndarray,
                            filters: Optional[dict] = None,
                            top_k: int = 10,
                            index: Optional[str] = None,
diff --git a/haystack/generator/transformers.py b/haystack/generator/transformers.py
index 4d4ed1ce5..a16e99e1c 100644
--- a/haystack/generator/transformers.py
+++ b/haystack/generator/transformers.py
@@ -166,7 +166,7 @@ class RAGenerator(BaseGenerator):
         return contextualized_inputs["input_ids"].to(self.device), \
                contextualized_inputs["attention_mask"].to(self.device)
 
-    def _prepare_passage_embeddings(self, docs: List[Document], embeddings: List[Optional[numpy.ndarray]]) -> torch.Tensor:
+    def _prepare_passage_embeddings(self, docs: List[Document], embeddings: List[numpy.ndarray]) -> torch.Tensor:
 
         # If document missing embedding, then need embedding for all the documents
         is_embedding_required = embeddings is None or any(embedding is None for embedding in embeddings)
diff --git a/haystack/reader/base.py b/haystack/reader/base.py
index e9d82c483..4a8b32790 100644
--- a/haystack/reader/base.py
+++ b/haystack/reader/base.py
@@ -28,10 +28,10 @@ class BaseReader(ABC):
         # the most significant difference between scores.
         # Most significant difference: a model switching from predicting an answer to "no answer" (or vice versa).
         # No_ans_gap is a list of this most significant difference per document
-        no_ans_gaps = np.array(no_ans_gaps)
-        max_no_ans_gap = np.max(no_ans_gaps)
+        no_ans_gap_array = np.array(no_ans_gaps)
+        max_no_ans_gap = np.max(no_ans_gap_array)
         # all passages "no answer" as top score
-        if (np.sum(no_ans_gaps < 0) == len(no_ans_gaps)):  # type: ignore
+        if np.sum(no_ans_gap_array < 0) == len(no_ans_gap_array):
             no_ans_score = best_score_answer - max_no_ans_gap  # max_no_ans_gap is negative, so it increases best pos score
         else:  # case: at least one passage predicts an answer (positive no_ans_gap)
             no_ans_score = best_score_answer - max_no_ans_gap
diff --git a/haystack/retriever/dense.py b/haystack/retriever/dense.py
index 45ae5cc4c..2a77d5ad9 100644
--- a/haystack/retriever/dense.py
+++ b/haystack/retriever/dense.py
@@ -210,7 +210,7 @@ class DensePassageRetriever(BaseRetriever):
             all_embeddings["query"] = np.concatenate(all_embeddings["query"])
         return all_embeddings
 
-    def embed_queries(self, texts: List[str]) -> List[np.array]:
+    def embed_queries(self, texts: List[str]) -> List[np.ndarray]:
         """
         Create embeddings for a list of queries using the query encoder
 
@@ -221,7 +221,7 @@ class DensePassageRetriever(BaseRetriever):
         result = self._get_predictions(queries)["query"]
         return result
 
-    def embed_passages(self, docs: List[Document]) -> List[np.array]:
+    def embed_passages(self, docs: List[Document]) -> List[np.ndarray]:
         """
         Create embeddings for a list of passages using the passage encoder
 
@@ -483,7 +483,7 @@ class EmbeddingRetriever(BaseRetriever):
                                                            top_k=top_k, index=index)
         return documents
 
-    def embed(self, texts: Union[List[str], str]) -> List[np.array]:
+    def embed(self, texts: Union[List[str], str]) -> List[np.ndarray]:
         """
         Create embeddings for each text in a list of texts using the retrievers model (`self.embedding_model`)
 
@@ -508,7 +508,7 @@ class EmbeddingRetriever(BaseRetriever):
             emb = [r for r in emb]
         return emb
 
-    def embed_queries(self, texts: List[str]) -> List[np.array]:
+    def embed_queries(self, texts: List[str]) -> List[np.ndarray]:
         """
         Create embeddings for a list of queries. For this Retriever type: The same as calling .embed()
 
@@ -517,7 +517,7 @@ class EmbeddingRetriever(BaseRetriever):
         """
         return self.embed(texts)
 
-    def embed_passages(self, docs: List[Document]) -> List[np.array]:
+    def embed_passages(self, docs: List[Document]) -> List[np.ndarray]:
         """
         Create embeddings for a list of passages. For this Retriever type: The same as calling .embed()
 
diff --git a/haystack/schema.py b/haystack/schema.py
index 8733f49a8..f1e7e8adf 100644
--- a/haystack/schema.py
+++ b/haystack/schema.py
@@ -11,7 +11,7 @@ class Document:
                  probability: Optional[float] = None,
                  question: Optional[str] = None,
                  meta: Dict[str, Any] = None,
-                 embedding: Optional[np.array] = None):
+                 embedding: Optional[np.ndarray] = None):
         """
         Object used to represent documents / passages in a standardized way within Haystack.
         For example, this is what the retriever will return from the DocumentStore,