Understanding ASCII Character Order

Characters compare using their code-point order: '0' < '9' < 'A' < 'Z' < 'a' < 'z' in ASCII. That is why sorting strings of digits lexicographically differs from sorting by numeric value ('10' < '2' as strings!).

Why this shows up in the real world

Version strings v9 vs v10 famously need custom parsers because naive string compare lies. Lexicographic file ordering in terminals follows character order byte-by-byte.

Core idea (explained for students)

Python compares strings lexicographically: first differing character decides; if one string is a prefix, shorter comes first. Tie this back to ord values for ASCII subsets.

Try this in Python

pairs = ["10", "2", "1", "20"]
print("lexicographic:", sorted(pairs))
print("numeric:", sorted(pairs, key=int))

Common mistakes

• Sorting numeric strings without padding ('007' tricks) or int keys.
• Assuming case-insensitive order—default is case-sensitive with uppercase before lowercase in ASCII.

Key takeaways

• When users see “alphabetical order,” clarify ASCII vs locale.
• For interviews, mention both sorted(list_of_str) and key functions.