String, list, dict methods and chaining

Learning objective

• Apply method calls and chaining to produce compact readable code.

Key syntax

let text: string = "  Lucia Lang  ";
let parts: list<string> = text.trim().lower().split(" ");

Examples

• String methods: upper, lower, trim, ltrim, rtrim, split, join, contains, starts_with, ends_with, replace, indexOf, repeat, substring, pad_left, pad_right, to_int, to_float, to_bool, count, capitalize, title, is_numeric, is_alpha, is_alnum.
• List methods: append, pop, contains, sort, reverse, indexOf, slice, clear, insert, remove, removeAt, extend, first, last, is_empty, copy.
• Dict methods: keys, values, contains_key, get, clear, remove, items, is_empty, size, merge, put.

Chaining examples

let cleaned: string = "  Lucia  ".trim().lower();
let words: list<string> = cleaned.split(" ");
let csv: string = ",".join(words);

let nums: list<int> = [3, 1, 2];
nums.sort();
let top2: list<int> = nums.slice(0, 2);
print(top2.contains(2));

Contracts to remember

• append takes exactly one item compatible with list<T>.
• pop takes no arguments.
• get accepts 1 or 2 arguments: key and optional default.
• insert requires (index: int, value: T).
• removeAt requires (index: int).
• extend requires list<T> compatible with receiver.
• put requires (key: K, value: V) compatible with dict type.
• Collection size uses len(x), not .length().

Cross-target note

• dict.get(key) differs when key is missing:

- Python target: returns None - JavaScript target: returns undefined

• dict.get(key, default) is consistent in both targets.

Common mistakes

• Calling methods that do not belong to the receiver type.
• Forgetting method argument contracts.

Suggested practice

• Normalize a list of names and build a CSV output line.

Related

• types-and-collections
• string-interpolation