# 1. Introduction

In Python, string manipulation is a common and essential skill. In this blog post, we'll explore how to merge two strings by inserting one string (s2) into the middle of another (s1). This technique is handy in various scenarios, from generating unique text patterns to solving algorithmic challenges.

# 2. Program Steps

1. Calculate the middle index of the first string (s1).

2. Slice the first string (s1) into two halves at the middle index.

3. Concatenate the first half of s1, the second string (s2), and the second half of s1 to form the new string.

# 3. Code Program

``````def append_in_middle(s1, s2):
# Step 1: Find the middle index of s1
middle_index = len(s1) // 2

# Step 2 & 3: Create the new string by concatenating the first half of s1, s2, and the second half of s1
new_string = s1[:middle_index] + s2 + s1[middle_index:]

return new_string

# Example usage
s1 = "hello"
s2 = "world"
result = append_in_middle(s1, s2)
print(result)  # Expected output: heworldllo
``````

### Output:

```heworldllo
```

### Explanation:

1. Middle Index Calculation (middle_index = len(s1) // 2): This line calculates the middle index of the string s1. Integer division (//) is used to ensure the result is an integer.

2. String Slicing (s1[:middle_index] and s1[middle_index:]): These expressions slice s1 into two halves. The first expression gives the first half, and the second gives the second half.

3. String Concatenation (s1[:middle_index] + s2 + s1[middle_index:]): This line concatenates the first half of s1, the entire s2, and the second half of s1 to form the new string.

By following these steps, we successfully insert s2 into the middle of s1.