Indexing, Slicing & f-Strings

beginner level · ~15 min · Module 3: Strings & String Operations

Extract characters with 0-based indexing, slice substrings with [start:stop:step], and format text with f-strings.

Learning objectives

  • Access individual string characters using positive and negative indices
  • Extract substrings using slice notation [start:stop:step]
  • Use f-strings for clean variable interpolation

Lesson material

Indexing & Slicing

Strings are ordered sequences of immutable characters.

  • Positive Index: Starts from 0 at the beginning.
  • Negative Index: Starts from -1 at the last character.
  • Slice Notation: string[start:stop:step] (stop index is EXCLUSIVE).

Example code

text = "PythonCode"

# Indexing
print("First char:", text[0])    # P
print("Last char:", text[-1])   # e

# Slicing
print("First 6 chars:", text[0:6])   # Python
print("Reversed:", text[::-1])        # edoCnohtyP

f-Strings (Formatted String Literals)

Prefix strings with f or F to embed Python expressions directly inside curly braces {}.

Example code

name = "Rimon"
score = 98.5
print(f"Student {name} achieved a score of {score}%.")

Practice exercise: String Slicing & Formatting

Given `word = "DEVELOPER"`, extract the substring `"DEV"` (first 3 chars) and print `f"Prefix: {sub}"`.

Test yourself with the Module 3: Strings & String Operations quiz →

View the full Python curriculum →