String Construction (repeat, pad, build from parts)

Construction turns a plan into text—repeat characters, interleave, pad to width, or build from numeric codes. Often combine chr/ord, ranges, and comprehension before a final join.

Why this shows up in the real world

Serial number generators format prefixes, counters, and checksum digits. ASCII art renderers place characters on a 2D grid then join rows.

Core idea (explained for students)

Think in stages: compute a list of lines or tokens, then join once. Padding: s.center(w) or f-string {name:>10}.

Try this in Python

def repeat_pattern(block: str, times: int) -> str:
    return block * times


print(repeat_pattern("ab", 3))

Common mistakes

• Building huge intermediate lists when a generator + streaming write would suffice.
• Off-by-one in repeat counts (n copies vs n separators).

Key takeaways

• Encode width and alignment rules in one formatting spec when possible.
• Unit-test empty and single-character constructions—they expose edge bugs.