Types, Truth, and Expressions
(Part 2)
Intro to Computer Science
CS1510
Dr. Sarah Diesburg
PA01
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From now on can use CONSTANT_NAMES for
constants
File names matter – give it the name that was
requested
No line wrap
Observations from PA 1
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Variable names matter (don’t call it
startingMileageStr when it contains a
number)
Why would you import math?
Why would you say float(2.2)
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Do your own work!
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Questions about PA02??
Line Wrap
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Some rules
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Strings must be closed in the line in which they
start
Adding a backslash at the end of the line tells
python that the command is continued on the end
of the line
5
Review : Python if Statement
if <expression> :
suite
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Evaluate the expression to a boolean value
(True or False)
if True, execute all statements in the suite
Review : Warning About
Indentation
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Elements of the “suite” must all be indented
the same number of spaces/tabs
Python only recognizes suites when they are
indented the same “distance”
You must be careful to get the indentation
right to get suites right.
Let’s test your knowledge
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Let‘s look at #1-4 in my questions.py
program…
Let’s test your knowledge
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Problems #1-4 : Which letters are printed?
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A
B
A and B
Neither
9
Let’s test your knowledge
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Let’s look at statements with if, elif, else
Problems #5-9 : Which letters are printed?
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
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A
B
A and B
Neither
Python Selection, Round 2
if boolean expression:
suite1
else:
The process is:
suite2
• evaluate the boolean
• if True, run suite1
• if False, run suite2
Python Selection, Round 3
if boolean expression1:
suite1
elif expression2:
The process is:
suite2
• evaluate expression1
• if True, run suite1
• If False, evaluate
expression 2
• if True, run suite2
Python Selection, Round 3
if boolean expression1:
suite1
elif boolean expression2:
suite2
#(as many elif’s as you want)
else:
suiteLast
if, elif, else, the Process
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Evaluate boolean expressions until:
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The boolean expression returns True
None of the boolean expressions return True
If a boolean returns True, run the
corresponding suite. Skip the rest of the if
If no boolean returns True, run the else suite,
the default suite
Compound Expressions
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Logical Operators (lower case)
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and
or
not
Let’s test your knowledge
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Problems #10-11 : Which letters are printed?
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
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A
B
A and B
Neither
Truth Tables
p
q
True
True
True
False
False
True
False
False
not p p and q
p or q
Truth Tables
p
q
not p
True
True
False
True
False
False
False
True
True
False
False
True
p and q
p or q
Truth Tables
p
q
not p
p and q
True
True
True
True
False
False
False
True
False
False
False
False
p or q
Truth Tables
p
q
not p
p and q
p or q
True
True
True
True
False
True
False
True
True
False
False
False
Truth Tables
p
q
not p
p and q
p or q
True
True
False
True
True
True
False
False
False
True
False
True
True
False
True
False
False
True
False
False
Chained Comparisons
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You are going to be tempted to write:
0 <= myInt <= 5
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But you will need to be very careful
Compound Evaluation
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Logically 0 < X < 3 is actually
(0 < X) and (X < 3)
Evaluate using X with a value of 2:
(0< X) and (X< 3)
Parenthesis first: (True) and (True)
Final value: True
(Note: parentheses are not necessary in this
case.)
Compound Evaluation
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BUT, I’ve seen students write:
3<X<0
Meaning they want to know if x is outside of that
range.
But this is actually
(3 < X) and (X < 0)
Evaluate using X with a value of 5:
(3< X) and (X< 0)
Parenthesis first: (True) and (False)
Final value: False