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Python If Statement: Selection Tool & Logic Expression Guide

Learn the primary selection tool in Python - the If statement - for making decisions based on test results. Discover examples of If, If...else, If...elif...else statements with logic expressions like equal, not equal, greater than, and less than.

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Python If Statement: Selection Tool & Logic Expression Guide

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  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 <test>: <statement>

  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 <test>: <statement1> else: <statement2>

  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 <test1>: <statement1> elif <test2>: <statement2> else: <statement3>

  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

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