Python - How to think like a computer scientist

Question 1

What is a “state snapshot”?

Answer 1

A more popular word (“most often referred to”) for reference diagram that maps variable names and values they refer to at a particular point in time

Question 2

Compare the error types between JavaScript and Python

Question 3

What does the line “import turtle” do?

Answer 3

load turtle module and associated types/objects (e.g. Turtle(), screen()

Question 4

define: instances. how do we create instances

Answer 4

copy of an object, independent of each other and has their own properties and methods

alex = turtle.Turtle()
tess = turtle.Turtle()

Question 5

give an example of a for loop and identify the different parts

Answer 5

example:

 for i in [item1, item 2, item3]: 
      print(i)

LOOP VARIABLE: i
LIST: [item1, item 2, item3]
LOOP BODY: print(i)

Question 6

define control flow

Answer 6

python keeping track of the code statement it’s executing, like a pointer finger

Question 7

what is a sequential control flow?

Answer 7

execution of code from top to bottom

Question 8

explain in flow chart how the for loop is a sequential control flow

Question 9

what’s another name for control flow

Answer 9

flow of execution

Question 10

how is the for loop a compound statement?

Answer 10

indentation

Question 11

what’s the general structure to print a range of numbers in an iteration?

Answer 11

range(start, stop, step)

Question 12

why do we need to wrap range in a list?

Answer 12

list(range()) - apparently range sometimes doesn’t print all the values

Question 13

what values would these statements give?

print(list(range(4)))
print(list(range(1, 5)))
print(list(range(1, 5, 2)))

Answer 13

[0, 1, 2, 3]
[1, 2, 3, 4]
[1, 3]

Question 14

identify method that allows us to turn a turtle negative angles or distances

Answer 14

turning a number negative produces the opposite of a specified direction

e.g. Turtle.forward(-100) moves it backward by 100
but you can also write this as Turtle.backward(100)

Question 15

identify method that allows turtle to pickup or put down pen

Answer 15

Turtle.up() / Turtle.penup()
Turtle.down() / Turtle.pendown()

Question 16

identify method that influences turtle shape, some shapes the turtle can take on

Answer 16

Turtle.shape(“”)

shapes = classic (pointer - think this is also the default), turtle, square, triangle, etc

Question 17

identify method that influences turtle’s animation speed

Answer 17

Turtle.speed()

Question 18

identify method to leave an imprint of the turtle shape on canvas

Answer 18

Turtle.stamp()

Question 19

what is programming?

Answer 19

“breaking up large task into tinier tasks that are generally made up of basic instructions”

Question 20

programs vs algorithms?

Answer 20

algorithm is a set of instructions but doesn’t necessarily need to be written in a language for the computer to interpret

a program is a set of instructions that needs to be more precise so the computer can follow

Question 21

compare interpreters and compilers

Answer 21

both converts high-level language (written to be readable by humans) to low-level language (machine/assembly language)

interpreter: alternates between converting and executing

compiler: converts entire source code before executing

Question 22

what does the compiler convert source code into (2 different words)

Answer 22

object code
executable

Question 23

what are a few common instructions (5) that appears in almost every programming language?

Answer 23

input
output
math & logic operations
conditions
repetition/iterations

Question 24

what are the 3 kinds of errors that can occur from human writing a program and give examples

Answer 24

(1) SYNTACTICAL ERROR
grammatical errors - caught by the machine before executing e.g. mispelling keywords, typos, forgetting a :

(2) RUNTIME ERROR
can only be caught after executing
e.g. trying to complete a computation

(3) SEMANTIC ERROR
program runs but. does something unexpected
trickier to solve, would need to retrace steps one by one

Question 25

natural vs formal language

Answer 25

NATURAL FORMAL
evolved over time designed for purpose
strict syntax
redundant precise
not literal (idioms etc) literal
ambiguous unambiguous

Question 26

what 2 types of syntax rules are there for languages? elaborate

Answer 26

tokens - language elements (or building blocks)
structure - how the tokens are arranged

Question 27

what are processes involved in understanding a language?

Answer 27

parsing - comprehending language structure
semantics - getting meaning from structure

Question 28

in python, everything is an _____

Answer 28

object, even a value that is a number or word is an object

Question 29

what other names are values known as?

Answer 29

classes/data types

Question 30

name 3 types of values

Answer 30

strings
floats - fractional numbers
integers - whole numbers

Question 31

how do we denote strings?

Answer 31

marked by single, double or triple quotes

Question 32

why can’t you put a comma to write 42000 like 42,000?

Answer 32

, is used to separate values so we would get the result “42 0”

Question 33

which function helps us identify what type an object is?

Answer 33

type([value here]) function

Question 34

how to convert types into another?

Answer 34

int()
float()
str()

Question 35

with int(), what’s something to note about this function? what happens if we’re trying to convert a non-numeric value?

Answer 35

finds the closest whole number - this is not the same as rounding up

e.g. int(53.785) will produce 53 not 54
.. so essentially, it’s rounding down?

Question 36

how to remind ourselves that assignment tokens does not mean equality?

Answer 36

whenever we write it, we don’t say to ourselves “a equals 2” but:
- a “refers to object” 2
- “reference to object”
- a “is assigned to” 2
- a “gets the value of” 2

Question 37

how can we track and diagram variables to their values

would like to revise this card when I see this tracked on more involved/complex problems

Answer 37

[attach diagram here]

Question 38

what are 5 naming conventions to keep in mind when making legal variable names in Python?

Answer 38

good_variable_name
variable$

(1) must begin with letter - conventional to use lowercase - or underscore, case sensitive
(2) no spaces
(3) the only special character that is safe is an underscore (i think). he says $ and + are not allowed but he doesn’t explicitly say all other characters other than underscore are illegal
(4) is not a reserved list of keywords Python already uses
(5) meaningful for other human readers of the program

Question 39

what is the primary difference between a statement and expression and give examples

Answer 39

STATEMENTS must be EXECUTED, they don’t return a value

FOR EXAMPLE:
assignment with =
while
for
if
import … e.g y = 3.14

EXPRESSIONS must be EVALUATED, they can contain values, variables, operators, function calls (e.g. print(y))

Question 40

what’s a way to tell if we’ve written a statement in the shell?

Answer 40

submitting a code line is followed by another prompt symbol rather than a value

note to self - insert pic later

Question 41

what is the operator for integer division? how is it different from division operator?

Answer 41

//

this returns only the integer after the calculation, kinda the opposite of what % does which is only return the remainder after division

Question 42

list order of precedence ** - + () * /

Answer 42

()
**
* /
- +

Question 43

which operators have the same precedence? what’s the formal name for the same precedence? what does this mean?

Answer 43

left-associative

• /
• +

Question 44

how is the exponentiation operator evaluated in this case 2 ** 3 ** 2?

Answer 44

right most exponent is evaluated first

Question 45

What is the value of the following expression: 16 - 2 * 5 // 3 + 1?

Answer 45

14

16 - (2 * 5 // 3) + 1
remember // is integer division

Question 46

what is the function to get user input?

Answer 46

input( “[default prompt string here]” )

Question 47

What is the key to being a successful programmer?

Answer 47

the ability to debug
keep up a momentum where successfully solving one problem motivates you to keep going

Question 48

What are the three key things to remember to avoid having to debug in the first place?

Answer 48

(1) understand the problem (and plan)
(2) get something small working first
(3) keep adding small working bits until you get a complete program

Question 49

What are the 2 most important clues you need to help you debug?

Answer 49

(1) error messages
(2) print statements - similar to “console.log”?

Question 50

Explain what these 4 common errors in Python you might get are and what debugging techniques might you use to solve them?

ParseError
NameError
TypeError
ValueError

Answer 50

ParseError - syntax errors

NameError - not initialising a variable before using it

TypeError - trying to combine different data types

ValueError - passing unexpected data through function?

Question 51

Compare the error types between JavaScript and Python