Characters, ord & chr Tricks

Every character your program reads is stored as a number under the hood. Knowing that code point lets you do math on letters. 🔢

The ord() function turns a single character into its integer code point. It is your bridge from letters into arithmetic.

The chr() function is the reverse: give it a number and it hands back the matching character. Together they form a clean round trip.

The big trick: a to z have consecutive code points, and so do A to Z. That means you can index letters with simple subtraction.

Subtract the base letter to get a clean 0-based index. This is how you turn a letter into an array slot for counting.

Going the other way, add the index to the base and call chr(). Now slot 0 becomes 'a' and slot 25 becomes 'z'.

To shift a letter forward, add the amount then wrap with modulo 26. This is the heart of a Caesar cipher problem.

Because of the layout, each uppercase letter sits exactly 32 below its lowercase twin. You can change case with pure arithmetic if you ever need to.

The character '7' is not the number 7. Subtract ord('0') to convert a digit character into its real numeric value.

For yes or no tests, methods like isalpha() and isdigit() are cleaner than comparing code points by hand.

Mapping letters to indices lets you use a tiny 26-slot array instead of a dictionary. That is faster and is a staple of string problems.

One quick question on letter math.

You learned that ord and chr convert letters to numbers and back, and that consecutive code points let you index, shift, and check characters with simple math. 🎉