A byte is eight bits, and it is the unit files and memory are counted in. Sizes grow in steps of a thousand-ish, which is why file sizes look the way they do.
About 2 min of reading
Measure sizes in bytes.
Show the wrap at the top of a byte.
Before you run it, say out loud what it will print. Then open the answer.
Print what two bytes hold.
Before you run it, say out loud what it will print. Then open the answer.
Count the bytes of a word.
Before you run it, say out loud what it will print. Then open the answer.
Print the thousand step.
Before you run it, say out loud what it will print. Then open the answer.
Read the first example one line at a time. A line that prints shows what appears on screen; the rest set things up quietly.
A machine points at bytes, not bits. A bit is inside a byte and can only be reached by masking, which is what later lessons do.
Sizes are powers of two because storage is binary. That is why a kilobyte is 1024 and not a round thousand.
print(256 % 256)
print(256 // 256)The two hundred fifty seventh value does not fit in one byte, so it carries into the next. That is the wrap at the top.
print(2 ** 16)Two bytes hold sixty five thousand five hundred thirty six values. Each byte added doubles the room by two hundred fifty six.
print(1024, 1024 * 1024)A kilobyte is 1024 bytes, a megabyte is 1024 of those. The step is 1024 because it is a power of two.
print(len("owlww".encode("utf-8")))Five plain letters are five bytes. One accented letter takes two, which is why sizes are not letter counts.
b = bytearray(4)
print(len(b))Memory is counted in bytes, not bits. A byte is the smallest piece a machine can point at on its own.
print(len(bytearray(1024 * 1024)))A megabyte is a million-ish bytes. Sizes that big are counted in steps, never in single bytes.
print(2 ** 10)One thousand twenty four is the power of two nearest a thousand. Binary counting makes that the natural step.
print(3 * 1024 * 1024)Three megabytes is three million-ish bytes. A download bar is that count divided into steps.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.