Spelling It Out: Progressive Substring List

1. The Challenge: Progressive Prefix Slicing

Create a function spelling(txt) that takes a word and spells it out by progressively building a list of substring prefixes. For example, "eats" should return ["e", "ea", "eat", "eats"].

2. Why It Matters

Building progressive prefixes is used in auto-complete search bars, prefix tree (trie) data structures, and type-ahead suggestions.

3. The Python Solution

Use a list comprehension slicing txt[:i] over range indices:

def spelling(txt):
    return [txt[:i] for i in range(1, len(txt) + 1)]

# Testing our function
print(spelling("eats"))   # Output: ['e', 'ea', 'eat', 'eats']
print(spelling("bee"))    # Output: ['b', 'be', 'bee']
print(spelling("happy"))  # Output: ['h', 'ha', 'hap', 'happ', 'happy']

4. How Slice txt[:i] Works

• When i = 1: txt[:1] extracts index 0 ("e").
• When i = 2: txt[:2] extracts indices 0 to 1 ("ea").
• When i = 4: txt[:4] extracts full word ("eats").

5. Common Mistakes

• Off-By-One Range Limit: Writing range(1, len(txt)) misses the final full word! Always use len(txt) + 1 to include the complete string slice.

6. Next Steps

Use txt[:i] for cumulative prefixes. Next, let's extract city facts from Python dictionaries!