diff --git a/Introduction-to-Data-Science/Week-4/Prajwal/reversing/input.txt b/Introduction-to-Data-Science/Week-4/Prajwal/reversing/input.txt
new file mode 100644
index 0000000..8ecb8d9
--- /dev/null
+++ b/Introduction-to-Data-Science/Week-4/Prajwal/reversing/input.txt
@@ -0,0 +1,3 @@
+hello
+i
+am
diff --git a/Introduction-to-Data-Science/Week-4/Prajwal/reversing/output.txt b/Introduction-to-Data-Science/Week-4/Prajwal/reversing/output.txt
new file mode 100644
index 0000000..31899b5
--- /dev/null
+++ b/Introduction-to-Data-Science/Week-4/Prajwal/reversing/output.txt
@@ -0,0 +1,2 @@
+babe
+hel
diff --git a/Introduction-to-Data-Science/Week-4/Prajwal/reversing/reverse.py b/Introduction-to-Data-Science/Week-4/Prajwal/reversing/reverse.py
new file mode 100644
index 0000000..17639de
--- /dev/null
+++ b/Introduction-to-Data-Science/Week-4/Prajwal/reversing/reverse.py
@@ -0,0 +1,23 @@
+file=open("input.txt",'r+')
+last=file.seek(0,2)
+lis=[0]
+ctr=0
+file.seek(0,0)
+i=0
+while i<last:
+	file.readline()
+	i=file.tell()
+	lis.append(i)
+	ctr+=1
+f=open("output.txt",'w+')
+dummy=ctr
+for i in range(dummy,0,-1):
+	file.seek(lis[i-1],0)
+	print(file.readline(),end="")
+	# below code is for writing it on another file called output
+	file.seek(lis[i-1],0)
+	f.write(file.readline())
+
+file.close()
+f.close()
+	
diff --git a/Introduction-to-Data-Science/Week-4/Prajwal/theory5.txt b/Introduction-to-Data-Science/Week-4/Prajwal/theory5.txt
new file mode 100644
index 0000000..73573c9
--- /dev/null
+++ b/Introduction-to-Data-Science/Week-4/Prajwal/theory5.txt
@@ -0,0 +1,13 @@
+ab+ mode opens the file for appending and reading in binary format.If the file exists , it opens in append mode and file pointer is at the end of the file. If the file does not exist, it creates a new file for reading and writing.
+
+when a file is read, data is transferred to an intermediate buffer before it can be accessed by python, therefore buffer parameter signifies the size in bytes of the buffer used while reading. -ve value indicates default buffer size, 0 indicates no buffering.
+
+try:
+	print(1/0)
+except ZeroDivisionError:
+	print("Number cannot be divided by zero")
+try:
+	print(1+"a")
+except :
+	print("cannot combine different data type with + in print function")
+
diff --git a/prajwalsb/Week-2/PrajwalSB/alternate.py b/prajwalsb/Week-2/PrajwalSB/alternate.py
new file mode 100644
index 0000000..8eb38b2
--- /dev/null
+++ b/prajwalsb/Week-2/PrajwalSB/alternate.py
@@ -0,0 +1,12 @@
+n= int(input("Enter: "))
+lists=[]
+for i in range(0,n):
+	x=int(input())
+	lists.append(x)
+print(len(lists))
+print("original list")
+print(lists)
+print("new list")
+for i in range(1,n,2):
+	del lists[(i+1)//2]
+print(lists)
diff --git a/prajwalsb/Week-2/PrajwalSB/pattern.py b/prajwalsb/Week-2/PrajwalSB/pattern.py
new file mode 100644
index 0000000..7fedfbf
--- /dev/null
+++ b/prajwalsb/Week-2/PrajwalSB/pattern.py
@@ -0,0 +1,18 @@
+n= int(input("Enter: "))
+for i in range(1,(n+1)):
+	for j in range(n,i,-1):
+		print("  ",end="")
+	for k in range(1,i):
+		print("* ",end="")
+	for l in range(0,i):
+		print("* ",end="")
+	print()
+
+for i in range(n-1,0,-1):
+	for j in range(0,n-i):
+		print("  ",end="")
+	for k  in range(1,(i*2)):
+		print("* ",end="")
+	print()
+	
+
diff --git a/prajwalsb/Week-2/PrajwalSB/sort.py b/prajwalsb/Week-2/PrajwalSB/sort.py
new file mode 100644
index 0000000..b283b74
--- /dev/null
+++ b/prajwalsb/Week-2/PrajwalSB/sort.py
@@ -0,0 +1,14 @@
+n= int(input("Enter: "))
+lists=[]
+for i in range(0,n):
+	x=int(input())
+	lists.append(x)
+
+for i in range(0,n-1):
+	for j in range(0,n-1-i):
+		if lists[j] > lists[j+1]:
+			temp =lists[j]
+			lists[j]=lists[j+1]
+			lists[j+1]=temp
+
+print(lists)
diff --git a/prajwalsb/Week-2/PrajwalSB/theory.txt b/prajwalsb/Week-2/PrajwalSB/theory.txt
new file mode 100644
index 0000000..6c7418f
--- /dev/null
+++ b/prajwalsb/Week-2/PrajwalSB/theory.txt
@@ -0,0 +1,17 @@
+Pros of python--
+easy to write the source code when compared with other languages.
+easily readable and understandable for a non-programmer.
+has a rich built-in and open source library
+useful for asynchronous codes.
+
+Cons of python---
+since its an interpreted language, its slower than many other languages
+it isn't used much in web browser and mobile computing
+Because the language is dynamically typed, it requires more testing and has errors
+
+The exponential operator has the highest priority in expression.
+
+// is called floor division operator.division that results into whole number adjusted to the left in the number line 
+ex: 5//3 will give 1 , 5/3 will give 1.6666667 
+    6//3 will give 2, 6/3 will give 2.0
+