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Understanding Python's IF Statement: Syntax and Logic Expressions

This chapter provides an in-depth understanding of Python's IF statement and logic expressions. It explains the syntax of IF statements and how Python evaluates truth using binary logic (1 for true, 0 for false). Examples illustrate the simple IF, IF-else, and nested IF statements along with common logic expressions such as equality, greater than, and and/or operations. A practical "login" scenario demonstrates how to use IF statements effectively. Ideal for beginners seeking to grasp conditional programming in Python.

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Understanding Python's IF Statement: Syntax and Logic Expressions

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  1. Chapter 9 IF Statement Dr. Bernard Chen Ph.D. University of Central Arkansas Spring 2012

  2. Outline • Logic expression • General concept behind the Python statement syntax • IF statement

  3. Some Logic Expression • Computer only understand ‘1’ and ‘0’ • In computer logic: • 1: true • 0: false

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

  5. Some Logic Expression example >>> a=10 >>> b=10 >>> a==b >>> a=10 >>> b=5 >>> a==b

  6. Some Logic Expression example >>> a=10 >>> b=10 >>> a!=b >>> a=10 >>> b=5 >>> a!=b

  7. Some Logic Expression example >>> a=10 >>> b=10 >>> a>=b >>> a=10 >>> b=5 >>> a<b

  8. Outline • Logic expression • General concept behind the Python statement syntax • IF statement

  9. Python’s Syntax • In general, Python has a simple syntax: • Block and statement boundaries are detected automatically: python use indention of statement under a header to group the statement • Header --- ‘:’

  10. Outline • Logic expression • General concept behind the Python statement syntax • IF statement • Simple If statement • If... else statement • If… else if … else statement

  11. 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

  12. Simple If statement • It takes the form of an if test • if <test>: <statement>

  13. 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”

  14. Truth Statement • In Python: • True means any nonzero number or nonempty object • False means not true: a zero number of empty object

  15. If Statement “login” example

  16. If... else statement • It takes the form of an if test, and ends with an optional else block • if <test>: <statement1> else: <statement2>

  17. If Statement “login” example

  18. If... else statement >>> a=10 >>> b=5 >>> if a>b: print “a is larger” else: print “b is larger”

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

  20. 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>

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

  22. If… else if … else statement example number = 23 guess = int(raw_input('Enter an integer : ')) if guess == number: print 'Congratulations, you guessed it.' print "(but you do not win any prizes!)" elif guess < number: print 'No, it is a little higher than that' else: print 'No, it is a little lower than that'

  23. In class practice import random number=random.randint(1,5) guess = int(raw_input('Enter an integer : ')) if guess == number: print 'Congratulations, you guessed it.' print "(but you do not win any prizes!)" elif guess < number: print 'No, it is a little higher than that' else: print 'No, it is a little lower than that' print 'The answer is:',number

  24. Some More Logic Expression • And (True if both are true) Examples: >>> 5>4 and 8>7 True >>> 5>4 and 8>9 False

  25. Example temp=int(raw_input("Please enter today's tempeture:")) rain=int(raw_input("Is is raining? 1:yes, 0:no")) if temp>86 and rain==0: print "Today is a hot sunny day" elif temp>86 and rain==1: print "Today is a hot raining day" elif temp<32 and rain==0: print "Today is a cold sunny day" elif temp<32 and rain==1: print "Today is a cold raining day" else: print "Today's weather is not special"

  26. Some More Logic Expression • Or (True if either one is true) Examples: >>> 5>4 or 8>7 True >>> 5>4 or 8>9 True

  27. Example a=10 b=20 if a%2==0 and b%2==0: print "Both a and b are even numbers" elif a%2==0 or b%2==0: print "Either a or b is an even number" else: print "Both a and b are odd numbers"

  28. Nested IF statement • Sometimes you may want to check one condition after another condition. In such situation, we call it “Nested IF Statement” • The Code would looks something like:

  29. Nested IF statement

  30. Example: deposit=int(raw_input('Clerk: How much do you want to deposit? ')) if deposit > 100000: print "Wow, that's a lot of money" if deposit < 500000: print "I need to call my manager" elif deposit < 1000000: print "Let me open an VIP room for you" else: print "Can you merry me?" elif deposit > 1000: print "Sure, let me do it right now, do you want to consider a CD" elif deposit > 1: print "Sure, let me do it right now" else: print "Are you kidding me, I am busy right now..."

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