diff --git a/src/pylast/__init__.py b/src/pylast/__init__.py
index 02db07c..1341de0 100644
--- a/src/pylast/__init__.py
+++ b/src/pylast/__init__.py
@@ -23,6 +23,7 @@ import collections
 import hashlib
 import html.entities
 import logging
+import os
 import shelve
 import ssl
 import tempfile
@@ -421,7 +422,8 @@ class _Network:
         """
 
         if not file_path:
-            file_path = tempfile.mktemp(prefix="pylast_tmp_")
+            self.cache_backend = _ShelfCacheBackend.create_shelf()
+            return
 
         self.cache_backend = _ShelfCacheBackend(file_path)
 
@@ -782,8 +784,11 @@ class LibreFMNetwork(_Network):
 class _ShelfCacheBackend:
     """Used as a backend for caching cacheable requests."""
 
-    def __init__(self, file_path=None):
-        self.shelf = shelve.open(file_path)
+    def __init__(self, file_path=None, flag=None):
+        if flag is not None:
+            self.shelf = shelve.open(file_path, flag=flag)
+        else:
+            self.shelf = shelve.open(file_path)
         self.cache_keys = set(self.shelf.keys())
 
     def __contains__(self, key):
@@ -799,6 +804,12 @@ class _ShelfCacheBackend:
         self.cache_keys.add(key)
         self.shelf[key] = xml_string
 
+    @classmethod
+    def create_shelf(cls):
+        file_descriptor, file_path = tempfile.mkstemp(prefix="pylast_tmp_")
+        os.close(file_descriptor)
+        return cls(file_path=file_path, flag="n")
+
 
 class _Request:
     """Representing an abstract web service operation."""
@@ -916,7 +927,7 @@ class _Request:
                     headers=headers,
                 )
             except Exception as e:
-                raise NetworkError(self.network, e)
+                raise NetworkError(self.network, e) from e
 
         else:
             conn = HTTPSConnection(context=SSL_CONTEXT, host=host_name)
@@ -924,7 +935,7 @@ class _Request:
             try:
                 conn.request(method="POST", url=host_subdir, body=data, headers=headers)
             except Exception as e:
-                raise NetworkError(self.network, e)
+                raise NetworkError(self.network, e) from e
 
         try:
             response = conn.getresponse()
@@ -937,7 +948,7 @@ class _Request:
                 )
             response_text = _unicode(response.read())
         except Exception as e:
-            raise MalformedResponseError(self.network, e)
+            raise MalformedResponseError(self.network, e) from e
 
         try:
             self._check_response_for_errors(response_text)
@@ -961,7 +972,7 @@ class _Request:
         try:
             doc = minidom.parseString(_string(response).replace("opensearch:", ""))
         except Exception as e:
-            raise MalformedResponseError(self.network, e)
+            raise MalformedResponseError(self.network, e) from e
 
         e = doc.getElementsByTagName("lfm")[0]
         # logger.debug(doc.toprettyxml())
@@ -1042,9 +1053,6 @@ class SessionKeyGenerator:
 
         if url in self.web_auth_tokens.keys():
             token = self.web_auth_tokens[url]
-        else:
-            # This will raise a WSError if token is blank or unauthorized
-            token = token
 
         request = _Request(self.network, "auth.getSession", {"token": token})
 
@@ -1397,7 +1405,13 @@ class _Taggable(_BaseObject):
         return seq
 
 
-class WSError(Exception):
+class PyLastError(Exception):
+    """Generic exception raised by PyLast"""
+
+    pass
+
+
+class WSError(PyLastError):
     """Exception related to the Network web service"""
 
     def __init__(self, network, status, details):
@@ -1441,7 +1455,7 @@ class WSError(Exception):
         return self.status
 
 
-class MalformedResponseError(Exception):
+class MalformedResponseError(PyLastError):
     """Exception conveying a malformed response from the music network."""
 
     def __init__(self, network, underlying_error):
@@ -1454,7 +1468,7 @@ class MalformedResponseError(Exception):
         )
 
 
-class NetworkError(Exception):
+class NetworkError(PyLastError):
     """Exception conveying a problem in sending a request to Last.fm"""
 
     def __init__(self, network, underlying_error):
@@ -2778,7 +2792,7 @@ def _collect_nodes(limit, sender, method_name, cacheable, params=None, stream=Fa
                     break  # success
                 except Exception as e:
                     if tries >= 3:
-                        raise e
+                        raise PyLastError() from e
                     # Wait and try again
                     time.sleep(1)
                     tries += 1
@@ -2795,7 +2809,7 @@ def _collect_nodes(limit, sender, method_name, cacheable, params=None, stream=Fa
                     main.getAttribute("totalPages") or main.getAttribute("totalpages")
                 )
             else:
-                raise Exception("No total pages attribute")
+                raise PyLastError("No total pages attribute")
 
             for node in main.childNodes:
                 if not node.nodeType == xml.dom.Node.TEXT_NODE and (
@@ -2910,9 +2924,6 @@ def _number(string):
 
 
 def _unescape_htmlentity(string):
-
-    # string = _unicode(string)
-
     mapping = html.entities.name2codepoint
     for key in mapping:
         string = string.replace("&%s;" % key, chr(mapping[key]))