diff --git a/deta/_async/client.py b/deta/_async/client.py
index f183253..18c21d5 100644
--- a/deta/_async/client.py
+++ b/deta/_async/client.py
@@ -6,16 +6,24 @@
 from urllib.parse import quote
 
 from deta.utils import _get_project_key_id
-from deta.base import FetchResponse, Util, insert_ttl, BASE_TTL_ATTTRIBUTE
+from deta.base import FetchResponse, Util, insert_ttl, BASE_TTL_ATTRIBUTE
 
 
-def AsyncBase(name: str):
+def AsyncBase(name: str, *, session: aiohttp.ClientSession = None):
     project_key, project_id = _get_project_key_id()
-    return _AsyncBase(name, project_key, project_id)
+    return _AsyncBase(name, project_key, project_id, session=session)
 
 
 class _AsyncBase:
-    def __init__(self, name: str, project_key: str, project_id: str, host: str = None):
+    def __init__(
+            self,
+            name: str,
+            project_key: str,
+            project_id: str,
+            *,
+            host: str = None,
+            session: aiohttp.ClientSession = None
+    ):
         if not project_key:
             raise AssertionError("No Base name provided")
 
@@ -23,9 +31,9 @@ def __init__(self, name: str, project_key: str, project_id: str, host: str = Non
         self._base_url = f"https://{host}/v1/{project_id}/{name}"
 
         self.util = Util()
-        self.__ttl_attribute = BASE_TTL_ATTTRIBUTE
+        self.__ttl_attribute = BASE_TTL_ATTRIBUTE
 
-        self._session = aiohttp.ClientSession(
+        self._session = session or aiohttp.ClientSession(
             headers={
                 "Content-type": "application/json",
                 "X-API-Key": project_key,
diff --git a/deta/base.py b/deta/base.py
index c15c127..706235c 100644
--- a/deta/base.py
+++ b/deta/base.py
@@ -1,6 +1,5 @@
 import os
 import datetime
-from re import I
 import typing
 from urllib.parse import quote
 
@@ -8,7 +7,7 @@
 
 # timeout for Base service in seconds
 BASE_SERVICE_TIMEOUT = 300
-BASE_TTL_ATTTRIBUTE = "__expires"
+BASE_TTL_ATTRIBUTE = "__expires"
 
 
 class FetchResponse:
@@ -131,7 +130,7 @@ def insert(
         if code == 201:
             return res
         elif code == 409:
-            raise Exception("Item with key '{4}' already exists".format(key))
+            raise Exception(f"Item with key '{key}' already exists")
 
     def put(
         self,
diff --git a/deta/service.py b/deta/service.py
index e1f1cdf..260bc16 100644
--- a/deta/service.py
+++ b/deta/service.py
@@ -81,16 +81,16 @@ def _request(
             res.read()
             if not self.keep_alive:
                 self.client.close()
-            ## return None if not found
+            # return None if not found
             if status == 404:
                 return status, None
             raise urllib.error.HTTPError(url, status, res.reason, res.headers, res.fp)
 
-        ## if stream return the response and client without reading and closing the client
+        # if stream return the response and client without reading and closing the client
         if stream:
             return status, res
 
-        ## return json if application/json
+        # return json if application/json
         payload = (
             json.loads(res.read())
             if JSON_MIME in res.getheader("content-type")
@@ -109,10 +109,10 @@ def _send_request_with_retry(
         body: typing.Union[str, bytes, dict] = None,
         retry=2,  # try at least twice to regain a new connection
     ):
-        reinitializeConnection = False
+        reinitialize_connection = False
         while retry > 0:
             try:
-                if not self.keep_alive or reinitializeConnection:
+                if not self.keep_alive or reinitialize_connection:
                     self.client = http.client.HTTPSConnection(
                         host=self.host, timeout=self.timeout
                     )
@@ -126,5 +126,5 @@ def _send_request_with_retry(
                 res = self.client.getresponse()
                 return res
             except http.client.RemoteDisconnected:
-                reinitializeConnection = True
+                reinitialize_connection = True
                 retry -= 1
diff --git a/deta/utils.py b/deta/utils.py
index f94c598..5bd127d 100644
--- a/deta/utils.py
+++ b/deta/utils.py
@@ -13,4 +13,4 @@ def _get_project_key_id(project_key: str = None, project_id: str = None):
     if project_id == project_key:
         raise AssertionError("Bad project key provided")
 
-    return project_key, project_id
\ No newline at end of file
+    return project_key, project_id