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Strings

String Slicing

Accessing substrings with slicing

Interview: Common interview topic

Last Updated: June 12, 2026 • 6 min read

Slicing is Python's powerful syntax for extracting substrings using the [start:stop:step] notation. It's one of the most frequently tested string topics in interviews.

Slicing Syntax

  • s[i] — single character at index i (0-based, negative counts from end)
  • s[start:stop] — substring from start to stop-1
  • s[start:stop:step] — every step-th character
  • s[:n] — first n characters
  • s[n:] — from index n to end
  • s[::-1] — reverse the string

Key Rules

  • Slicing never raises IndexError — out-of-range indices are handled gracefully
  • stop is exclusive: s[0:3] gives indices 0, 1, 2
  • Negative indices count from end: s[-1] is the last character
  • Negative step reverses direction: s[::-1] reverses the entire string
  • Slicing creates a new string object (shallow copy for strings)

Use Cases

Reversing strings for palindrome checking

Extracting substrings for text parsing

Skipping characters with step slicing

Safe substring extraction without index bounds checking

Common Mistakes

Forgetting that stop index is exclusive (off-by-one errors)

Confusing negative indices with step direction

Thinking slicing modifies the original string (it creates a new one)

Not knowing that out-of-range slices return empty strings instead of raising errors