Iteration “for ??? in range(min,max,interval):” What if we do not know the number of repetitions ? “while (???):” (p.49) problem = input(“Enter a math problem, or ‘q’ to quit: “) while (problem != “q”): print(“Answer to “, problem, “ is: “, eval(problem)) problem = input(“Enter a math problem, or ‘q’ to quit: “)

Chap. 5 Conditional Expressions Can test equality with == Can also test, >=, <=, != (not equals) In general, 0 is false, 1 is true  So you can have a function return a “true” or “false” value. Alert! = means “make them equal!” == means “are they equal?”

Multiple conditionals (Boolean) A and B A or B True only when both True when either A and B are true A or B is true B\A False True B\A False True False False False False False True True False True True True True not A

Boolean Operators and, or, not 6<10 and 3<7 4!=4 or 5<8 not 6<10

If..else Conditional def posSum(list): psum = 0 for v in range(0, len(list)): if list[v] > 0: psum = psum+list[v] return psum Add all values in a list Add only positive values def sum(list): psum = 0 for v in range(0, len(list)): psum = psum + list[v] return psum

How an if works if is the command name Next comes an expression: Some kind of true or false comparison Then a colon Then the body of the if—the things that will happen ONLY WHEN the expression is true if list[v] > 0 : psum = psum+list[v]

if (expression): next indented block else: Statements false Pictorial view of how if works true

Conditional Drunken turtle Random walk or Brownian motion A turtle From the current position Take an arbitrary direction and distance

Random package import random random.random() returns a random fraction between 0 and 1 How to get a random number between (0,100)? A random number between (-50, 50) ?

Drunken Turtle Present location of turtle: curX, curY Next random location ? nextX = curX * random.random() nextY = curY * random.random()

Random Walk import random # # function randNext(curX, curY) # Given coordinate (curX, curY), generate next random coordinate # def randNext(curX, curY): nextX = curX *random.random() nextY = curY *random.random() return nextX, nextY

How to write a function for repetitive operations ? Repeated set of instructions (curX, curY) = (nextX, nextY) (nextX, nextY) = randWalk.randNext(curX, curY) tt.goto(nextX, nextY) Write a function, called drawRandom(), that performs the repeated set of instructions

What is a potential problem ? May run out of the display window How can we make it sure that turtle stays in bound ?

Lab Write a Python function of a drunken turtle which stays in bound wn = turtle.getscreen() wWid = wn.window_width() wHgt = wn.window_height() Make it sure that you halve the window sizes for +- coordinates your Python program