String Comparison (order, equality, casefold keys)

Comparing strings uses lexicographic order (<, >) like a dictionary: first differing character decides; if one is a prefix, shorter is smaller. Equality is ==; identity is is—do not confuse them.

Why this shows up in the real world

Version sorting tweaks string compare rules (10 after 2 unless padded). Git orders paths lexicographically in tree objects.

Core idea (explained for students)

Python compares strings element-wise by Unicode code points. For human sorting, locale.strcoll or libraries handle locale rules.

Try this in Python

print("apple" < "apply", "a" < "aa", sorted(["b", "A", "a"], key=str.casefold))

Common mistakes

• Case-sensitive vs insensitive—normalize first.
• Comparing None to string without guard.

Key takeaways

• For sort keys, pack tuples (primary, tie_breaker) instead of concatenating strings blindly.
• Use key=str.casefold in sorted for case-insensitive ordering.