Programming I: First Programs in Python

A program is an ordered list of statements the computer carries out exactly, one after another from top to bottom.

A variable is a name bound to a value, and every value carries a type — int, float, str, or bool — that fixes what can be done with it.

print() sends text to the screen while input() reads one line back from the person, always handing it over as a string.

An expression combines values and operators into a single computed value, evaluated under fixed precedence rules.

Comparison operators and the connectives and, or, and not reduce values to True or False — the two answers every decision is built on.

An if / elif / else statement runs exactly one branch, chosen by the first boolean test that comes out True.

A while loop repeats its body as long as a condition stays true, so the body must eventually make that condition false.

A for loop binds a variable to each item a sequence like range() hands it, running the body exactly once per item.

Tracing a loop line by line in a table reveals how the counter grows and where an off-by-one boundary error slips in.

Defining a function stores a named block of steps, and calling that name runs those steps wherever you invoke it.

Parameters carry values into a function and the return statement hands one value back out to the caller.

A function's local names are private to its own call, which lets you break a large problem into small, independently testable parts.

A list is an ordered, index-addressed, mutable collection of values you can read, grow, change, and loop across.

A string is an immutable indexed sequence of characters you can slice, search, and rebuild into new strings.

A single pass through a sequence with an accumulator variable can find the maximum, count matches, or search for a value.

Debugging is a repeatable method: read the traceback, locate the failing line, form a single hypothesis, and test it.