1. Chapter 9 IF Statement Bernard Chen

2. If Statement The main statement used for selecting from alternative actions based on test results It’s the primary selection tool in Python and represents the Logic process

3. Some Logic Expression Equal: “==” NOT Equal: “!=” Greater: “>”, “>=” Less than: “<”, “<=”

4. Outline Simple If statement If... else statement If… else if … else statement

5. Simple If statement It takes the form of an if test if :

6. Simple If statement if 4>3: print “it is true that 4>3” if 1: print “true” a=10 if a==10: print “a=10”

7. If... else statement It takes the form of an if test, and ends with an optional else block if : else:

8. If... else statement if 3>4: print “3 is larger than 4” else: print “3 is NOT larger than 4” if 0: print “true” else: print “false”

9. If... else statement a=10 if a==10: print “a=10” else: print “a is not equal to 10” a=10 if a!=10: print “a=10” else: print “a is not equal to 10” (also try >, < )

10. If… else if … else statement It takes the form of an if test, followed by one or more optional elif tests, and ends with an optional else block if : elif : else:

11. If… else if … else statement a=10 if a>10: print “a > 10” elif a==10: print “a = 10” else: print “a < 10”

12. If… else if … else statement example number = 23 guess = int(raw_input('Enter an integer : ')) if guess == number: print 'Congratulations, you guessed it.' # New block starts here print "(but you do not win any prizes!)" # New block ends here elif guess < number: print 'No, it is a little higher than that' # Another block # You can do whatever you want in a block... else: print 'No, it is a little lower than that' # you must have guess > number to reach here

13. Some More Logic Expression and >>> 5>4 and 8>7 True >>> 5>4 and 8>9 False

14. Some More Logic Expression or >>> 5>4 or 8>7 True >>> 5>4 or 8>9 True