point polygon rectangle text graphwin methods summary gregorian epact gui hailstone function halting problem happy happy birthday lyrics problem description program happy py hard drive hardware hash array hierarchy chartsee structure chart house house (of representatives) identifier definition of rules for forming idle if statement flowchart semantics syntax if-elif-else statement semantics syntax if-else statement decision tree nested semantics syntax image implementation import statement with "from" import statement indefinite loop indexing dictionary from the right list negative indexes string infinite loop inheritance inner product innerprod input validation input statement multiple values semantics syntax input/output devices instance instance variable accessing instance variable and object state int automatic conversion to float literal range of representation integer division interest calculation program interface interpreter diagram python vs compiler intractable problems investment doubling ipo (inputprocessoutput) iteration key cipher private public shared with dictionary key-value pair keyerror keywords koch curve