diff --git a/python_ifirma/core.py b/python_ifirma/core.py
index 9773bb2..6b22c8f 100644
--- a/python_ifirma/core.py
+++ b/python_ifirma/core.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+
 import six
 import json
 import datetime
@@ -50,17 +51,17 @@ class Client:
             "Ulica": self.address.street,
             "Miejscowosc": self.address.city,
             "Kraj": self.address.country,
-            #"Email": self.email,
-            #"Telefon": self.phone_number,
+            # "Email": self.email,
+            # "Telefon": self.phone_number,
             "OsobaFizyczna": False,
         }
         if self.export == "eu":
             d.update({"PrefiksUE": self.tax_id[:2]})
         if self.export == "eu" or self.export == "yes":
             d.update({"NIP": self.tax_id[2:]})
-            #if self.export == "eu":
-            #d.update({"PrefiksUE": self.tax_id[:2]})
-            #elif self.export == "yes":
+            # if self.export == "eu":
+            #    d.update({"PrefiksUE": self.tax_id[:2]})
+            # elif self.export == "yes":
             d.update({"Kraj": self.tax_id[:2]})
         else:
             d.update({"NIP": self.tax_id})
@@ -147,7 +148,7 @@ class NewInvoiceParams:
             d.update({
                 "DataObowiazkuPodatkowego": self.__get_issue_date(),
                 "NazwaUslugi": "services",
-                "Waluta": self.currency, #"PLN",
+                "Waluta": self.currency,
                 "Jezyk": "en",
                 "KursWalutyWidoczny": False,
                 "KursWalutyZDniaPoprzedzajacegoDzienWystawieniaFaktury": 1.00,
@@ -195,7 +196,7 @@ class iFirmaAPI():
 
         return response_dict
 
-    def __create_authentication_header_value(self, request_hash_text, key_value=""):
+    def __get_auth_header(self, request_hash_text, key_value=""):
         key_value = key_value or self.__invoice_key_value
         return "IAPIS user={}, hmac-sha1={}".format(
             self.__username,
@@ -215,7 +216,7 @@ class iFirmaAPI():
         headers = {
             "Accept": "application/json",
             "Content-type": "application/json; charset=UTF-8",
-            "Authentication": self.__create_authentication_header_value(request_hash_text)
+            "Authentication": self.__get_auth_header(request_hash_text)
         }
 
         response_dict = self.__execute_post_request(headers, request_content, url)
@@ -253,11 +254,33 @@ class iFirmaAPI():
             "Accept": "application/json",
             "Content-type": "application/json; charset=UTF-8",
             "Authentication":
-            self.__create_authentication_header_value(request_hash_text, self.__user_key_value)
+            self.__get_auth_header(request_hash_text, self.__user_key_value)
         }
-        resp = requests.get(url, headers=headers)
-        content = resp.content
-        return content
+        response = requests.get(url, headers=headers)
+        resp = json.loads(response.content.decode("utf-8"))
+
+        month = resp['response']["MiesiacKsiegowy"]
+        year = resp['response']['RokKsiegowy']
+        return year, month
+
+    def list_invoices(self):
+        url = 'https://www.ifirma.pl/iapi/faktyury.json'
+        request_hash_text = "{}{}{}".format(
+            url,
+            self.__username,
+            self.__user_key_name,
+        )
+        headers = {
+            "Accept": "application/json",
+            "Content-type": "application/json; charset=UTF-8",
+            "Authentication":
+            self.__get_auth_header(request_hash_text, self.__user_key_value)
+        }
+        response = requests.get(url, headers=headers)
+        resp = json.loads(response.content.decode("utf-8"))
+
+        return resp
+
 
     def __post_cost(self, cost_json, url):
         request_content = json.dumps(cost_json, separators=(',', ':'))
@@ -270,7 +293,7 @@ class iFirmaAPI():
         headers = {
             "Accept": "application/json",
             "Content-type": "application/json; charset=UTF-8",
-            "Authentication": self.__create_authentication_header_value(request_hash_text)
+            "Authentication": self.__get_auth_header(request_hash_text)
         }
 
         response_dict = self.__execute_post_request(headers, request_content, url)
@@ -291,7 +314,7 @@ class iFirmaAPI():
         headers = {
             "Accept": "application/json",
             "Content-type": "application/json; charset=UTF-8",
-            "Authentication": self.__create_authentication_header_value(request_hash_text)
+            "Authentication": self.__get_auth_header(request_hash_text)
         }
         params = {}
         if limit:
@@ -301,7 +324,7 @@ class iFirmaAPI():
         return rj
 
     def get_invoice(self, invoice_id):
-        url = "https://www.ifirma.pl/iapi/fakturaeksportuslug/{}.json".format(invoice_id)
+        url = f"https://www.ifirma.pl/iapi/fakturaeksportuslug/{invoice_id}.json"
         request_hash_text = "{}{}{}".format(
             url,
             self.__username,
@@ -310,7 +333,7 @@ class iFirmaAPI():
         headers = {
             "Accept": "application/json",
             "Content-type": "application/json; charset=UTF-8",
-            "Authentication": self.__create_authentication_header_value(request_hash_text)
+            "Authentication": self.__get_auth_header(request_hash_text)
         }
         resp = requests.get(url, headers=headers)
         rj = json.loads(resp.content.decode('utf-8'))
@@ -320,11 +343,11 @@ class iFirmaAPI():
             return rj
 
     def get_invoice_pdf(self, invoice_id):
-        url = "https://www.ifirma.pl/iapi/fakturakraj/{}.pdf".format(invoice_id)
+        url = f"https://www.ifirma.pl/iapi/fakturakraj/{invoice_id}.pdf"
         return self.__download_pdf(url)
 
     def __get_invoice_number(self, invoice_id):
-        url = "https://www.ifirma.pl/iapi/fakturakraj/{}.json".format(invoice_id)
+        url = f"https://www.ifirma.pl/iapi/fakturakraj/{invoice_id}.json"
         request_hash_text = "{}{}{}".format(
             url,
             self.__username,
@@ -333,7 +356,7 @@ class iFirmaAPI():
         headers = {
             "Accept": "application/json",
             "Content-type": "application/json; charset=UTF-8",
-            "Authentication": self.__create_authentication_header_value(request_hash_text)
+            "Authentication": self.__get_auth_header(request_hash_text)
         }
         resp = requests.get(url, headers=headers)
         rj = json.loads(resp.content.decode('utf-8'))
@@ -351,7 +374,7 @@ class iFirmaAPI():
         headers = {
             "Accept": "application/pdf",
             "Content-type": "application/pdf; charset=UTF-8",
-            "Authentication": self.__create_authentication_header_value(request_hash_text)
+            "Authentication": self.__get_auth_header(request_hash_text)
         }
         resp = requests.get(url, headers=headers)
 
diff --git a/setup.py b/setup.py
index 2eaee35..31ca603 100644
--- a/setup.py
+++ b/setup.py
@@ -2,7 +2,7 @@ from setuptools import setup, find_packages
 
 setup(
     name="python-ifirma",
-    version="0.0.5",
+    version="0.1.0",
     packages=find_packages(),
     install_requires=[
         'requests',
@@ -12,4 +12,4 @@ setup(
     author_email='dariusz@aniszewski.eu',
     license='BSD License',
 
-)
\ No newline at end of file
+)