diff --git a/FourmiCrawler/sources/ChemSpider.py b/FourmiCrawler/sources/ChemSpider.py
index 87a6ee7..fb51a4a 100644
--- a/FourmiCrawler/sources/ChemSpider.py
+++ b/FourmiCrawler/sources/ChemSpider.py
@@ -26,9 +26,12 @@ class ChemSpider(Source):
     structure = 'Chemical-Structure.%s.html'
     extendedinfo = 'MassSpecAPI.asmx/GetExtendedCompoundInfo?csid=%s&token='
 
-    def __init__(self, config={}):
+    def __init__(self, config=None):
         Source.__init__(self, config)
-        self.cfg = config
+        if self.cfg is None:
+            self.cfg = {}
+        else:
+            self.cfg = config
         self.ignore_list = []
         if 'token' not in self.cfg or self.cfg['token'] == '':
             log.msg('ChemSpider token not set or empty, search/MassSpec API '
diff --git a/FourmiCrawler/sources/NIST.py b/FourmiCrawler/sources/NIST.py
index 3c323ef..d71d08f 100644
--- a/FourmiCrawler/sources/NIST.py
+++ b/FourmiCrawler/sources/NIST.py
@@ -22,12 +22,13 @@ class NIST(Source):
 
     search = 'cgi/cbook.cgi?Name=%s&Units=SI&cTP=on'
 
-    cfg = {}
-
-    def __init__(self, config={}):
+    def __init__(self, config=None):
         Source.__init__(self, config)
         self.ignore_list = set()
-        self.cfg = config
+        if config is None:
+            self.cfg = {}
+        else:
+            self.cfg = config
 
     def parse(self, response):
         sel = Selector(response)
diff --git a/FourmiCrawler/sources/WikipediaParser.py b/FourmiCrawler/sources/WikipediaParser.py
index 4aa49b2..b995f30 100644
--- a/FourmiCrawler/sources/WikipediaParser.py
+++ b/FourmiCrawler/sources/WikipediaParser.py
@@ -1,9 +1,11 @@
+import re
+
 from scrapy.http import Request
 from scrapy import log
-from source import Source
 from scrapy.selector import Selector
+
+from source import Source
 from FourmiCrawler.items import Result
-import re
 
 
 class WikipediaParser(Source):
@@ -17,11 +19,13 @@ class WikipediaParser(Source):
     __spider = None
     searched_compounds = []
 
-    cfg = {}
 
-    def __init__(self, config={}):
+    def __init__(self, config=None):
         Source.__init__(self, config)
-        self.cfg = config
+        if config is None:
+            self.cfg = {}
+        else:
+            self.cfg = config
 
     def parse(self, response):
         """
diff --git a/FourmiCrawler/sources/source.py b/FourmiCrawler/sources/source.py
index a609bb9..fe36784 100644
--- a/FourmiCrawler/sources/source.py
+++ b/FourmiCrawler/sources/source.py
@@ -6,7 +6,7 @@ class Source:
     website = "http://something/*"  # Regex of URI's the source is able to parse
     _spider = None
 
-    def __init__(self, config={}):
+    def __init__(self, config=None):
         """
         Initiation of a new Source
         """
diff --git a/FourmiCrawler/spider.py b/FourmiCrawler/spider.py
index 5c09f07..7552c7d 100644
--- a/FourmiCrawler/spider.py
+++ b/FourmiCrawler/spider.py
@@ -10,7 +10,7 @@ class FourmiSpider(Spider):
     """
     name = "FourmiSpider"
 
-    def __init__(self, compound=None, selected_attributes=[".*"], *args, **kwargs):
+    def __init__(self, compound=None, selected_attributes=None, *args, **kwargs):
         """
         Initiation of the Spider
         :param compound: compound that will be searched.
@@ -20,7 +20,10 @@ class FourmiSpider(Spider):
         self.synonyms = set()
         super(FourmiSpider, self).__init__(*args, **kwargs)
         self.synonyms.add(compound)
-        self.selected_attributes = selected_attributes
+        if selected_attributes is None:
+           self.selected_attributes = [".*"]
+        else:
+            self.selected_attributes = selected_attributes
 
     def parse(self, response):
         """