String Traversal and Character Access in DSA Python

Mental Model

A string is a sequence of characters you can look at one by one from start to end.

Analogy: Like reading a sentence letter by letter to understand or find a specific word.

"H" -> "e" -> "l" -> "l" -> "o" -> null
 ↑

Dry Run Walkthrough

Input: string: "Hello", print each character one by one

Goal: To visit and print each character in the string in order

Step 1: Start at the first character 'H'

"H" -> "e" -> "l" -> "l" -> "o" -> null
 ↑

Why: We begin reading from the first character

Step 2: Print 'H' and move to next character 'e'

"H" -> "e" -> "l" -> "l" -> "o" -> null
    ↑

Why: We print current character and move forward to continue traversal

Step 3: Print 'e' and move to next character 'l'

"H" -> "e" -> "l" -> "l" -> "o" -> null
       ↑

Why: Continue printing each character in order

Step 4: Print 'l' and move to next character 'l'

"H" -> "e" -> "l" -> "l" -> "o" -> null
          ↑

Why: Keep moving forward to print all characters

Step 5: Print 'l' and move to next character 'o'

"H" -> "e" -> "l" -> "l" -> "o" -> null
             ↑

Why: Almost at the end, print each character

Step 6: Print 'o' and reach end of string

"H" -> "e" -> "l" -> "l" -> "o" -> null
                ↑

Why: Last character printed, traversal complete

Result:

"H" -> "e" -> "l" -> "l" -> "o" -> null
Printed characters: H e l l o

Annotated Code

DSA Python

class StringTraversal:
    def __init__(self, text: str):
        self.text = text

    def traverse_and_print(self):
        for i in range(len(self.text)):
            print(self.text[i], end=' ')

if __name__ == '__main__':
    s = StringTraversal("Hello")
    s.traverse_and_print()

for i in range(len(self.text)):

loop through each index from 0 to length-1 to access characters in order

print(self.text[i], end=' ')

print character at current index without newline to show sequence

Output

H e l l o 

Complexity Analysis

Time: O(n) because we visit each character once where n is string length

Space: O(1) because no extra space is used besides loop variables

vs Alternative: Direct indexing is simpler and faster than converting string to list first

Edge Cases

empty string ""

loop does not run, nothing is printed

DSA Python

for i in range(len(self.text)):

string with one character "A"

prints single character 'A' correctly

DSA Python

for i in range(len(self.text)):

When to Use This Pattern

When you need to process or examine each character in a string one by one, use string traversal to access characters by their position.

Common Mistakes

Mistake: Trying to modify characters directly in the string (strings are immutable)
Fix: Use a new string or list to store changes instead of changing original string

Mistake: Using incorrect index range causing index out of range error
Fix: Always loop from 0 to len(string)-1 using range(len(string))

Summary

It visits each character in a string one by one in order.

Use it when you want to read or process every character in a string.

Remember strings are like a chain of characters you can access by position starting at zero.