Strings & Text Processing — Lesson 2: Take a slice of a string

New skill: Slicing, bounds and uppercasing
Previously learned: Units 01–06

Why this matters

Apps create short category tags, previews, and IDs from longer names.

Step 1 — Explore working Python

Read the program below. Before running it, write down the result you expect.

word = 'playground'
print(word[:4])
print(word[4:])
print(word[:4].upper())

Step 2 — Trace the code

1. Read word[:4] as characters from the beginning up to, but not including, index 4.
2. Change the ending index and compare the outputs.
3. Apply .upper() to a slice to create an uppercase code.

Step 3 — Check your understanding

Predict 'coding'[1:4]. Which letters does Python include?

Step 4 — Watch for this mistake

A slice uses an exclusive end position. [:3] takes three characters, not four.

Practice: Take a slice of a string

Complete short_code(text) to return the first three characters of text in uppercase. Inputs contain at least three characters.

Function contract: short_code(text)
Starter file: main.py

Work in the editor, using Run to explore and Check to compare against the published examples. Your submitted code, not the public check, determines the recorded score.

Hint 1 — Start

Use a slice that starts at the beginning.

Hint 2 — Build

Remember that the stop index is excluded.

Hint 3 — Test

Call the string method `.upper()` on the slice.

Reflect

In 3–5 sentences, explain the algorithm you chose, one test case you predicted, and how you would detect an incorrect answer.

Optional reading

For another perspective on this skill, see How to Think Like a Computer Scientist (interactive textbook). This Playground lesson, worked example, and exercise are original; no textbook passages were reproduced.