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

ConditionalDrunken turtle

Random walk or Brownian motionA turtle

From the current positionTake an arbitrary direction and distance

Random packageimport 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 -50 + 100* random.random()nextY = curY -50 + 100* random.random()

Random Walk

import random

## function randNext(curX, curY)# Given coordinate (curX, curY), generate next

random coordinate#def randNext(curX, curY): nextX = curX -50 + 100*random.random() nextY = curY -50 + 100*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

Email your Python program 2015fall91.100@gmail.com