empty string sentinel end-of-file loop from file with readlines interactive loop negative sentinel average two numbers average py average py average py average py average py average py avg py babysitting base conversion batch processing example program binary binary search bit black box blackjack bmi (body mass index) boolean algebra (logic) expression operator values break statement implementing post-test loop style considerations bridge (card game) brooksfred bug butterfly effect button class definition description methods button py byte code -curve caesar cipher calculator problem description program cannonball algorithm graphical display problem description program projectile class card deck of cball py cball py cball py cbutton cd celsius censor change counter program change py change py chaos discussion - program chaos py chr christmas cipher ciphertext circle constructor methods circle area formula intersection with line class class standing class statement classes button calculator dice dieview graphicsinterface msdie player pokerapp projectile projectile as module file rballgame