diff --git a/store/eval.py b/store/eval.py
index 9ca42b3..505b589 100755
--- a/store/eval.py
+++ b/store/eval.py
@@ -34,7 +34,7 @@ def locate(fname, namespace=''):
 
 def open_sim(directory, maxcache=None):
     tr = None
-    if len(glob(os.path.join(directory, 'nojump.xtc'))) is 1:
+    if len(glob(os.path.join(directory, 'nojump.xtc'))) == 1:
         tr = md.open(directory, trajectory='nojump.xtc', cached=maxcache, reindex=True)
     else:
         tr = md.open(directory, trajectory='out/*.xtc', cached=maxcache, reindex=True, nojump=True)
diff --git a/store/store.py b/store/store.py
index b6cd8d6..b3a29f9 100755
--- a/store/store.py
+++ b/store/store.py
@@ -123,7 +123,7 @@ class Simulation(Base):
     def __repr__(self):
         attrs = []
         for attr, val in self.__dict__.items():
-            if attr[0] is not '_' and attr is not 'type':
+            if attr[0] != '_' and attr != 'type':
                 attrs.append('{}={}'.format(attr, val))
         return '<{classname}({attributes})>'.format(classname=self.__class__.__name__, attributes=', '.join(attrs))
 
@@ -208,7 +208,7 @@ class Evaluation(Base):
     def __repr__(self):
         attrs = []
         for attr, val in self.__dict__.items():
-            if attr[0] is not '_' and attr not in ['type', 'data']:
+            if attr[0] != '_' and attr not in ['type', 'data']:
                 attrs.append('{}={}'.format(attr, val))
         return '<{classname}({attributes})>'.format(classname=self.__class__.__name__, attributes=', '.join(attrs))
 
@@ -227,7 +227,7 @@ def float_query(value, dbattr):
         crit = dbattr == float(value)
     elif isinstance(value, str):
         limits = value.split('-')
-        if len(limits) is 2:
+        if len(limits) == 2:
             try:
                 limits = [float(x) for x in limits]
             except:
diff --git a/store/utils.py b/store/utils.py
index 922cfac..0c8c854 100755
--- a/store/utils.py
+++ b/store/utils.py
@@ -30,7 +30,7 @@ def number_shorthand(x):
         return True
     elif isinstance(x, str):
         limits = x.split('-')
-        if len(limits) is 2:
+        if len(limits) == 2:
             try:
                 limits = [float(a) for a in limits]
             except: