1. Unit 3: Python
Lesson 3: Boolean Logic
January 5, 2014

2. Lesson 3: Boolean Logic
Introduction to
Programming
Lesson 1
Designing a
Game
Lesson 8
Sorting and
Searching
Lesson 9
Hardware &
Software
Lesson 2
Working with
Files
Lesson 7
Advanced
Algorithms
Lesson 10
Boolean Logic
Lesson 3
Loops
Lesson 6
Navigating the
Web (?)
Lesson 11
Functions
Lesson 4
Data Types
Lesson 5
Putting It All
Together
Lesson 12
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3. Recap from last time (I)
• Software is electronically stored data that allows us to interact with
our devices
• Hardware is the physical device that we need to interact with our
computer programs
• You can think of software and hardware as two pieces that come
together to make the finished product that we use such as browsing
Google, writing a Word document, or playing Angry Birds on our
iPhone
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4. Recap from last time (II)
• Our computer hardware needs software called an operating system
in order to function
• Updating software occurs much more frequently than updating
hardware
• Software communicates with hardware through programming
languages
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5. Computers use a very simple vocabulary
• While computers can be programmed to do some amazing things,
they only know a few simple words
• Today, we will look at some of the basic vocabulary that computers
rely upon
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6. TRUE and FALSE are the most basic words a
computer will use
• To a computer, the answer to any question will either be TRUE or
FALSE. If a computer asked you if you were hungry, you wouldn’t
say “Yes” or “No” – you would say “TRUE” or “FALSE”
• Using TRUE and FALSE is how computers think, and it’s called
Boolean logic after George Boole, a 19th Century English
mathematician
Are you
hungry?
TRUE
George Boole
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7. Combine words with AND, NOT, and OR
• Computers also love to use the words “AND”, “NOT”, and “OR”, but
their meanings can be a little different from how we would use them
• Let’s imagine a restaurant where the menu has only three items
Fish
Chips
Mushy Peas
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8. AND means “both”
• “AND” is used just like we would say “And” in English
• If a computer asked if you were hungry for “Fish AND Chips”, it
would want to know if you wanted “Fish and Chips both”
Fish AND
Chips?
Fish and Chips
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9. NOT means “Everything except”
• “NOT” to computers is a little different from the English “Not”
• If a computer asked if you were hungry for “NOT Fish”, it would want
to know if you wanted “Everything except Fish”
• Since there are only three items on the menu, this means “Chips
and Mushy Peas”
NOT Fish?
+
Chips
Mushy Peas
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10. Remember that OR is a little different (I)
• In English, asking if you want “Fish or Chips” is the same as asking
if you want:
Either
or
Fish only
Chips only
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11. Remember that OR is a little different (II)
• In English, asking if you want “Fish or Chips” is the same as asking
if you want:
or
Fish only
Chips only
• But to a computer, asking if you want “Fish OR Chips” is equivalent
to asking if you want:
or
Fish only
or
Chips only
Fish and Chips
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12. See if you can figure these out on your own
1. Fish AND Chips AND Mushy Peas
1. NOT Mushy Peas
1. Fish OR Mushy Peas
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13. Did you get them right?
1. Fish AND Chips AND Mushy Peas
1. NOT Mushy Peas
Fish and Chips and Mushy Peas
Fish and Chips
1. Fish OR Mushy Peas
or
Fish only
or
Mushy Peas only
Fish and Mushy Peas
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14. Let’s see a few more examples
• This time, let’s imagine that the menu has four items for breakfast
Bacon
Eggs
Toast
Tea
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15. Combining AND, NOT, and OR can get messy!
1. NOT Tea
2. NOT (Toast AND Tea)
3. Bacon OR Eggs OR Tea
4. (Bacon AND Eggs) OR Toast
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16. How did you do?
1. NOT Tea
Bacon, Eggs, and Toast
3. Bacon OR Eggs OR Tea
2. NOT (Toast AND Tea)
Bacon and Eggs
4. (Bacon AND Eggs) OR Toast
or
Any combination of
Bacon, Eggs, and Tea
Bacon and Eggs
or
Toast only
Bacon, Eggs,
and Toast
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17. This vocabulary is useful in IF statements (II)
• IF statements allow a computer to behave differently under different
situations
• In the examples below, you’ll see how IF statements use the
vocabulary we just learned
IF statement
if “you are tired”:
“go rest for a while”
Explanation
If “you are tired” is TRUE,
then “go rest for a while”
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18. This vocabulary is useful in IF statements (II)
• IF statements allow a computer to behave differently under different
situations
• In the examples below, you’ll see how IF statements use the
vocabulary we just learned
IF statement
if “you are tired”:
“go rest for a while”
if “you are tired” OR “you are sick”:
“go rest for a while”
Explanation
If “you are tired” is TRUE,
then “go rest for a while”
If “you are tired” is TRUE, or
If “you are sick” is TRUE, or
If “you are tired and sick” is TRUE,
then “go rest for a while”
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19. You can turn an IF into an IF-ELSE (I)
• We can start with a regular IF statement like in the example below
IF-ELSE statement
Explanation
if “the water looks clean”:
“drink it”
If “the water looks clean” is TRUE,
then “drink it”.
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20. You can turn an IF into an IF-ELSE (II)
• By adding an ELSE, you can decide what happens when the IF
statement is FALSE
IF-ELSE statement
Explanation
if “the water looks clean”:
“drink it”
If “the water looks clean” is TRUE,
then “drink it”.
else:
“buy bottled water”
If “the water looks clean” is FALSE,
then “buy bottled water”
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21. You can even make it an IF-ELIF-ELSE (I)
• Sometimes you will have more than two cases to choose from. In
these situations, you first start with a regular IF statement
IF-ELIF-ELSE statement
if “Manchester United scored more
goals than Liverpool”:
“Manchester United wins!”
Explanation
If “Manchester United scored more
goals than Liverpool” is TRUE,
then “Manchester United wins!”
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22. You can even make it an IF-ELIF-ELSE (II)
• Then we can add on an ELIF to check for a second case
IF-ELIF-ELSE statement
Explanation
if “Manchester United scored more
goals than Liverpool”:
“Manchester United wins!”
If “Manchester United scored more
goals than Liverpool” is TRUE,
then “Manchester United wins!”
elif “Liverpool scored more goals
than Manchester United”:
“Liverpool wins!”
If “Liverpool scored more goals
than Manchester United” is TRUE,
then “Liverpool wins!”
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23. You can even make it an IF-ELIF-ELSE (III)
• Finally, we can use an ELSE to handle any other cases
IF-ELIF-ELSE statement
Explanation
if “Manchester United scored more
goals than Liverpool”:
“Manchester United wins!”
If “Manchester United scored more
goals than Liverpool” is TRUE,
then “Manchester United wins!”
elif “Liverpool scored more goals
than Manchester United”:
“Liverpool wins!”
If “Liverpool scored more goals
than Manchester United” is TRUE,
then “Liverpool wins!”
else:
“Break the tie with penalty kicks”
If both statements are FALSE,
then “Use penalty kicks to break
the tie”
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24. Summary (I)
• Boolean Logic is a phrase used to describe the way computers think
only in TRUE and FALSE
• AND, NOT, and OR can be used to combine statements together,
but their meanings are a little different from their English meanings
• Remember that OR means one, or the other, or both!
or
Fish only
or
Chips only
Fish and Chips
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25. Summary (II)
• IF statements allow a computer to perform differently when in
different situations
• Add ELSE to decide what will happen when the IF statement is
FALSE
• Add ELIF when you have more than two cases to choose from
Manchester United wins!
Liverpool wins!
Penalty kicks
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26. What to do on your own
1. Go to URL to complete the Codecademy course online
2. Do the practice set on the material learned
1. Take the follow-up quiz to test your understanding
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