diff --git a/etherscan/accounts.py b/etherscan/accounts.py
index d9e3264..2bf7177 100644
--- a/etherscan/accounts.py
+++ b/etherscan/accounts.py
@@ -4,7 +4,7 @@
 
 class Account(Client):
     PAGE_NUM_PATTERN = re.compile(
-        '[1-9](?:\d{0,2})(?:,\d{3})*(?:\.\d*[1-9])?|0?\.\d*[1-9]|0')
+        r'[1-9](?:\d{0,2})(?:,\d{3})*(?:\.\d*[1-9])?|0?\.\d*[1-9]|0')
 
     def __init__(self, address=Client.dao_address, api_key='YourApiKeyToken'):
         Client.__init__(self, address=address, api_key=api_key)
diff --git a/etherscan/client.ropsten.py b/etherscan/client.ropsten.py
index 5e86661..a4fbdcc 100644
--- a/etherscan/client.ropsten.py
+++ b/etherscan/client.ropsten.py
@@ -30,12 +30,12 @@ class BadRequest(ClientException):
     """Invalid request passed"""
 
 
-#  Assume user puts his API key in the api_key.json file under variable name "key"
+# API key must be in the api_key.json file under variable name "key"
 class Client(object):
     dao_address = '0xbb9bc244d798123fde783fcc1c72d3bb8c189413'
 
     # Constants
-    PREFIX = 'https://api-ropsten.etherscan.io/api?'  # TESTNET 
+    PREFIX = 'https://api-ropsten.etherscan.io/api?'  # TESTNET
     MODULE = 'module='
     ACTION = '&action='
     CONTRACT_ADDRESS = '&contractaddress='
@@ -101,7 +101,8 @@ def __init__(self, address, api_key=''):
             self.url_dict[self.ADDRESS] = address
 
     def build_url(self):
-        self.url = self.PREFIX + ''.join([param + val if val else '' for param, val in self.url_dict.items()])
+        self.url = self.PREFIX + ''.join(
+            [parm + val if val else '' for parm, val in self.url_dict.items()])
 
     def connect(self):
         # TODO: deal with "unknown exception" error
@@ -119,14 +120,15 @@ def connect(self):
                     return data
                 else:
                     raise EmptyResponse(data.get('message', 'no message'))
-        raise BadRequest("Problem with connection, status code: %s" % req.status_code)
+        raise BadRequest(
+            f"Problem with connection, status code: {req.status_code}")
 
     def check_and_get_api(self):
         if self.url_dict[self.API_KEY]:  # Check if api_key is empty string
             pass
         else:
-            self.url_dict[self.API_KEY] = input('Please type your EtherScan.io API key: ')
+            self.url_dict[self.API_KEY] = input(
+                'Please type your EtherScan.io API key: ')
 
     def check_keys_api(self, data):
-        return all (k in data for k in ('jsonrpc', 'id', 'result'))
-    
\ No newline at end of file
+        return all(k in data for k in ('jsonrpc', 'id', 'result'))
diff --git a/etherscan/contracts.py b/etherscan/contracts.py
index df02a8a..9b07d62 100644
--- a/etherscan/contracts.py
+++ b/etherscan/contracts.py
@@ -16,4 +16,4 @@ def get_sourcecode(self):
         self.url_dict[self.ACTION] = 'getsourcecode'
         self.build_url()
         req = self.connect()
-        return req['result']
\ No newline at end of file
+        return req['result']
diff --git a/tests/test_accounts.py b/tests/test_accounts.py
index 138f738..12a17a6 100644
--- a/tests/test_accounts.py
+++ b/tests/test_accounts.py
@@ -2,18 +2,25 @@
 
 from etherscan.accounts import Account
 
-SINGLE_BALANCE = '40807168566070000000000'
+SINGLE_BALANCE = '40807178566070000000000'
 SINGLE_ACCOUNT = '0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a'
-MULTI_ACCOUNT = ['0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a',
-           '0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a']
+MULTI_ACCOUNT = [
+    '0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a',
+    '0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a',
+]
 MULTI_BALANCE = [
-    {'account': '0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a', 
-     'balance': '40807168566070000000000'},
-    {'account': '0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a', 
-    'balance': '40807168566070000000000'}
+    {
+        'account': '0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a',
+        'balance': '40807178566070000000000'
+    },
+    {
+        'account': '0xddbd2b932c763ba5b1b7ae3b362eac3e8d40121a',
+        'balance': '40807178566070000000000',
+    }
 ]
 API_KEY = 'YourAPIkey'
 
+
 class AccountsTestCase(unittest.TestCase):
 
     def test_get_balance(self):
@@ -22,4 +29,4 @@ def test_get_balance(self):
 
     def test_get_balance_multi(self):
         api = Account(address=MULTI_ACCOUNT, api_key=API_KEY)
-        self.assertEqual(api.get_balance_multiple(), MULTI_BALANCE)
\ No newline at end of file
+        self.assertEqual(api.get_balance_multiple(), MULTI_BALANCE)