diff --git a/backtracking/Remove_Invalid_Parenthesis.py b/backtracking/Remove_Invalid_Parenthesis.py
index 8b5a29dc9..862006d7f 100644
--- a/backtracking/Remove_Invalid_Parenthesis.py
+++ b/backtracking/Remove_Invalid_Parenthesis.py
@@ -1,50 +1,52 @@
 def isParenthesis(c):
-	return ((c == '(') or (c == ')')) 
+    return (c == "(") or (c == ")")
+
 
 def isValidString(str):
-	cnt = 0
-	for i in range(len(str)):
-		if (str[i] == '('):
-			cnt += 1
-		elif (str[i] == ')'):
-			cnt -= 1
-		if (cnt < 0):
-			return False
-	return (cnt == 0)
-	
-# method to remove invalid parenthesis 
+    cnt = 0
+    for i in range(len(str)):
+        if str[i] == "(":
+            cnt += 1
+        elif str[i] == ")":
+            cnt -= 1
+        if cnt < 0:
+            return False
+    return cnt == 0
+
+
+# method to remove invalid parenthesis
 def removeInvalidParenthesis(str):
-	if (len(str) == 0):
-		return
-		
-	visit = set()
-	
-	q = []
-	temp = 0
-	level = 0
-	
-	q.append(str)
-	visit.add(str)
-	while(len(q)):
-		str = q[0]
-		q.pop(0)
-		if (isValidString(str)):
-			print(str)
-			
-			level = True
-		if (level):
-			continue
-		for i in range(len(str)):
-			if (not isParenthesis(str[i])):
-				continue
-				
-			temp = str[0:i] + str[i + 1:] 
-			if temp not in visit:
-				q.append(temp)
-				visit.add(temp)
+    if len(str) == 0:
+        return
+
+    visit = set()
+
+    q = []
+    temp = 0
+    level = 0
+
+    q.append(str)
+    visit.add(str)
+    while len(q):
+        str = q[0]
+        q.pop(0)
+        if isValidString(str):
+            print(str)
+
+            level = True
+        if level:
+            continue
+        for i in range(len(str)):
+            if not isParenthesis(str[i]):
+                continue
+
+            temp = str[0:i] + str[i + 1 :]
+            if temp not in visit:
+                q.append(temp)
+                visit.add(temp)
+
 
 expression = "()())()"
 removeInvalidParenthesis(expression)
 expression = "()v)"
 removeInvalidParenthesis(expression)
-