life after cs106ap!web.stanford.edu/class/archive/cs/cs106ap/cs106ap.1198/... · 2019. 7. 1. ·...
TRANSCRIPT
Life after CS106AP!
Day 1!
Life after CS106AP!
Day 1!
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Ask yourself if all of the conditions always need to be checked!
not and or
● not and or○ not boolean_expression
○ boolean_expression_a and boolean_expression_b
○ boolean_expression_a or boolean_expression_b
if ___________:
# Do something
elif ___________:
# Do something different
else:
# Do something else
if ___________:
# Do something
else:
# Do something else
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Image (c) 2019 HP Development Company, L.P. [source]
Variables!
Definition
Definition
Think of them as labels for containers!
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Python objects are stored on RAM
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num_flowers = 5
num_flowers = 5
num_flowers = 5
=
Definition
num_flowers = 5
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Definition i.e. attaching it to the bag
num_flowers = 5
variable’s name
num_flowers = 5
variable’svalue
num_flowers = 5
num_flowers = 5num_picked = 2
num_flowers = 5num_picked = 2num_flowers = num_flowers – num_picked
num_flowers = 5num_picked = 2num_flowers = num_flowers – num_picked
Think/Pair/Share: Try to predict what happens here!
num_flowers = 5 num_picked = 2 num_flowers = num_flowers – num_picked
variable assignment!
num_flowers = 5 num_picked = 2 num_flowers = num_flowers – num_picked
The right side of the equals sign always gets evaluated first.
num_flowers = 5 num_picked = 2 num_flowers = num_flowers – num_picked
variable retrieval!
num_flowers = 5 num_picked = 2 num_flowers = num_flowers – num_picked
Definition
num_flowers = 5 num_picked = 2 num_flowers = num_flowers – num_picked
The right side of the equals sign always gets evaluated first.
num_flowers = 5 num_picked = 2 num_flowers = num_flowers – num_picked
We get the values using variable retrieval (i.e. checking what suitcase is attached).
5 2
num_flowers = 5 num_picked = 2 num_flowers = num_flowers – num_picked
Then we can evaluate the right hand side of the assignment.
5 2
num_flowers = 5 num_picked = 2 num_flowers = num_flowers – num_picked
Then we can evaluate the right hand side of the assignment.
5 2
3
num_flowers = 5 num_picked = 2 num_flowers =
The right side of the equals sign always gets evaluated first.
3
num_flowers = 5 num_picked = 2 num_flowers =
This is a new Python object!
3
num_flowers = 5 num_picked = 2 num_flowers =
Python handles all the baggage for you when you use variables.
3
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Style note
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num_flowers = 5
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5 is an integer
num_flowers = 5
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5 is an integer
num_flowers = 5
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5.0 is a float(has decimals)
num_flowers = 5.0
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num_flowers = 5
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fraction = 0.2
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fraction = 0.2
Called “doubles” in some other languages
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is_raining_today = True
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Talk to your neighbor!
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type(x)
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● type(x)
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Literals are Python objectswritten directly in code, e.g. the 5 in num_flowers = 5
()
*, /, //, %
+, -
()
*, /, //, %
+, -
Ties within rows are broken by going from left to right
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Talk with a partner!
()
*, /, //, %
+, -
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()
*, /, //, %
+, -
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()
*, /, //, %
+, -
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NOTE: Any of the literals can also be replaced with variables that are associated with the same value
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For example:
x = 24 + x * 3
This evaluates to 10, just like our first example expression!
The resulting expression always evaluates to true or false (but the operators don’t need to compare two booleans).
Therefore, we can use the resulting expression as the condition in if statements and while loops!
()
*, /, //, %
+, -
<, <=, >, >=, ==, !=
()
*, /, //, %
+, -
<, <=, >, >=, ==, !=
Ties still broken by going left to right!
()
*, /, //, %
+, -
<, <=, >, >=, ==, !=
What if the operator isn’t built in?
math
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math
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○ math.sqrt(4)
math
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○ math.sqrt(4)
Name of library
Library function
math
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○ math.sqrt(4)
● import math
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math
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○ math.sqrt(4)
● import math
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● math
○ math.sqrt(value)
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● math
print()
def print_my_variables():
x = 5
y = 2
print(x)
print(y)
print(x + y)
print()
def print_my_variables():
x = 5
y = 2
print(x)
print(y)
print(x + y)
print()
def print_my_variables():
x = 5
y = 2
print(x)
print(y)
print(x + y)
NOTE: Variables only exist in the function in which they’re created
print()
def print_my_variables():
x = 5
y = 2
print(x)
print(y)
print(x + y)
print() displays the value of what’s inside the parentheses
print()
def print_my_variables():
x = 5
y = 2
print(x)
print(y)
print(x + y)
In functions, we can’t just type x or y directly like we did in the interpreter.
print()
def print_my_variables():
x = 5
y = 2
print(x)
print(y)
print(x + y)
We’ll go into more depth about print() later this week!
Constants!
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MY_CONSTANT = 500
Style note
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Constants!
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Life after CS106AP!
Day 1!