diff --git a/Behavioral/chain_of_responsibility.py b/Behavioral/chain_of_responsibility.py
index 77923a1..95b8115 100644
--- a/Behavioral/chain_of_responsibility.py
+++ b/Behavioral/chain_of_responsibility.py
@@ -42,7 +42,7 @@ class ConcreteHandlerA(Handler):
 
     def handle_request(self, request):
         if 0 <= request < 10:
-            print("%s process %s" % (self.__class__.__name__, request))
+            print(f"{self.__class__.__name__} process {request}")
         else:
             self.successor.handle_request(request)
 
@@ -56,7 +56,7 @@ class ConcreteHandlerB(Handler):
 
     def handle_request(self, request):
         if 10 <= request < 20:
-            print("%s process %s" % (self.__class__.__name__, request))
+            print(f"{self.__class__.__name__} process {request}")
         else:
             self.successor.handle_request(request)
 
@@ -70,7 +70,7 @@ class ConcreteHandlerC(Handler):
 
     def handle_request(self, request):
         if 20 <= request < 30:
-            print("%s process %s" % (self.__class__.__name__, request))
+            print(f"{self.__class__.__name__} process {request}")
         else:
             self.successor.handle_request(request)
 
diff --git a/Behavioral/interpreter.py b/Behavioral/interpreter.py
index e779f00..14ef6ab 100644
--- a/Behavioral/interpreter.py
+++ b/Behavioral/interpreter.py
@@ -79,8 +79,7 @@ def output(self, value):
 if __name__ == '__main__':
     context = Context("in", "out")
 
-    l = []
-    l.append(TerminalExpression())
+    l = [TerminalExpression()]
     l.append(TerminalExpression())
     l.append(NoterminalExpression())
 
diff --git a/Behavioral/iterator.py b/Behavioral/iterator.py
index 247f34d..b01f692 100644
--- a/Behavioral/iterator.py
+++ b/Behavioral/iterator.py
@@ -80,12 +80,11 @@ def __iter__(self):
 
 
     def __next__(self):
-        if self.i < self.n:
-            i = self.i
-            self.i += 1
-            return i
-        else:
+        if self.i >= self.n:
             raise StopIteration()
+        i = self.i
+        self.i += 1
+        return i
 
 
 if __name__ == '__main__':
diff --git a/Behavioral/observer.py b/Behavioral/observer.py
index 80d5251..541ff93 100644
--- a/Behavioral/observer.py
+++ b/Behavioral/observer.py
@@ -71,7 +71,7 @@ def __init__(self, subject, name):
 
     def update(self):
         self.objserver_staus = self.subject.status
-        print("the observer: %s status change to %s" % (self.name , self.objserver_staus))
+        print(f"the observer: {self.name} status change to {self.objserver_staus}")
 
 
 if __name__ == '__main__':
diff --git a/Behavioral/visitor.py b/Behavioral/visitor.py
index 8470a8d..f589c01 100644
--- a/Behavioral/visitor.py
+++ b/Behavioral/visitor.py
@@ -37,12 +37,14 @@ class ConcreteVisitor1(Visitor):
     """
 
     def visitor_concrete_element_a(self, concrete_element_a):
-        print("%s visit %s" % (self.__class__.__name__,
-                               concrete_element_a.__class__.__name__))
+        print(
+            f"{self.__class__.__name__} visit {concrete_element_a.__class__.__name__}"
+        )
 
     def visitor_concrete_element_b(self, concrete_element_b):
-        print("%s visit %s" % (self.__class__.__name__,
-                               concrete_element_b.__class__.__name__))
+        print(
+            f"{self.__class__.__name__} visit {concrete_element_b.__class__.__name__}"
+        )
 
 
 class ConcreteVisitor2(Visitor):
@@ -53,12 +55,14 @@ class ConcreteVisitor2(Visitor):
     """
 
     def visitor_concrete_element_a(self, concrete_element_a):
-        print("%s visit %s" % (self.__class__.__name__,
-                               concrete_element_a.__class__.__name__))
+        print(
+            f"{self.__class__.__name__} visit {concrete_element_a.__class__.__name__}"
+        )
 
     def visitor_concrete_element_b(self, concrete_element_b):
-        print("%s visit %s" % (self.__class__.__name__,
-                               concrete_element_b.__class__.__name__))
+        print(
+            f"{self.__class__.__name__} visit {concrete_element_b.__class__.__name__}"
+        )
 
 
 class Element(metaclass=ABCMeta):
diff --git a/Creational/abstract_factory.py b/Creational/abstract_factory.py
index f2ae442..f5f3793 100644
--- a/Creational/abstract_factory.py
+++ b/Creational/abstract_factory.py
@@ -20,7 +20,7 @@ def __init__(self, name):
         self.name = name
 
     def __str__(self):
-        return "ProductA: %s" % self.name
+        return f"ProductA: {self.name}"
 
 
 class ConcreteProductA1(AbstractProductA):
@@ -39,7 +39,7 @@ def __init__(self, name):
         self.name = name
 
     def __str__(self):
-        return "ProductB: %s" % self.name
+        return f"ProductB: {self.name}"
 
 
 class ConcreteProductB1(AbstractProductB):
diff --git a/Creational/builder.py b/Creational/builder.py
index ecd4791..eef0a42 100644
--- a/Creational/builder.py
+++ b/Creational/builder.py
@@ -30,7 +30,7 @@ def add(self, part):
         self.__parts.append(part)
 
     def show(self):
-        print('-'.join(item for item in self.__parts))
+        print('-'.join(self.__parts))
 
 
 class Builder(metaclass=ABCMeta):
diff --git a/Creational/singleton.py b/Creational/singleton.py
index 55cb6c1..cff712d 100644
--- a/Creational/singleton.py
+++ b/Creational/singleton.py
@@ -22,9 +22,7 @@ def __init__(self, *args, **kwargs):
     def __call__(self, *args, **kwargs):
         if self.__instance is None:
             self.__instance=super().__call__(*args,**kwargs)
-            return self.__instance
-        else:
-            return self.__instance
+        return self.__instance
 
 
 # Python3
diff --git a/Structural/flyweight.py b/Structural/flyweight.py
index d027527..d34535b 100644
--- a/Structural/flyweight.py
+++ b/Structural/flyweight.py
@@ -52,7 +52,7 @@ class FlyweightFactory(object):
     """
 
     def __init__(self):
-        self.__flyweights = dict()
+        self.__flyweights = {}
 
         fx = ConcreteFlyweight()
         self.__flyweights["X"] = fx