Input and output functions and control statements

input() reads a line from the keyboard and always returns a string, so convert it with int() or float() before arithmetic. print() accepts sep (placed between items) and end (placed after the last item, default newline). Formatting uses f-strings such as f"{x:.2f}" or "{:>5}".format(s); .2f means two decimals and >5 right-aligns in width 5.

Control flow uses if/elif/else, for over any iterable, and while. range(start, stop, step) stops before stop. break leaves a loop, continue skips to the next pass and pass does nothing. A loop's else block runs only if the loop finished without break. After a for loop the loop variable keeps its last value; if the iterable was empty it is never created.

Truthiness: 0, 0.0, '', [], {}, () and None are falsy; every other value, including the string '0', is truthy. A conditional expression is written a if cond else b.

Exam trap: the else of a loop is not an else for the loop's if. It runs when no break happened, which surprises most beginners.