CSCI Fall 2018 Midterm

Question 1

conditional execution

Answer 1

instruction check for certain conditions, and run their accompanying code

Question 2

repetition

Answer 2

instruction to perform some action repeatedly, usually with some variation

Question 3

Python interpreter

Answer 3

program that reads and executes python code

Question 4

> > >

Answer 4

prompt. telling you that interpreter is ready for you to enter code

Question 5

*

Answer 5

multiply

Question 6

**

Answer 6

62 = 36
33=27
exponent

Question 7

ctrl + z

Answer 7

zombies the program. stops it in its track

Question 8

kill %n

Answer 8

kills the nth job–use carefully

Question 9

value

Answer 9

one of the basic things a program works with, like a letter or a number. Some
values we have seen so far are 2, 42.0, and ‘Hello, World!’.

Question 10

type

Answer 10

integers, floating-point numbers, strings

Question 11

type()

Answer 11

gives you what type of value is inside the parentheses

Question 12

prompt

Answer 12

Characters displayed by the interpreter to indicate that it is ready to take input
from the user.

Question 13

interpreter

Answer 13

A program that reads another program and executes it

Question 14

program

Answer 14

A set of instructions that specifies a computation

Question 15

Operator

Answer 15

A special symbol that represents a simple computation like addition, multiplication,
or string concatenation.

Question 16

int

Answer 16

type
integer
whole number

Question 17

float

Answer 17

type

numbers with fractional parts

Question 18

string

Answer 18

sequence of charachters

Question 19

syntax

Answer 19

rules that govern structure of program

Question 20

assignment statement

Answer 20

creates a new variable and gives it a value:
»> message = ‘And now for something completely different’
»> n = 17
»> pi = 3.141592653589793

Question 21

Python key words

Answer 21

False class finally is return
None continue for lambda try
True def from nonlocal while
and del global not with
as elif if or yield
assert else import pass
break except in raise

Question 22

string concatenation

Answer 22

The + operator performs string concatenation, which means it joins the strings by linking
them end-to-end. For example:
>>> first = 'throat'
>>> second = 'warbler'
>>> first + second
throatwarbler

Question 23

syntax error

Answer 23

“Syntax” refers to the structure of a program and the rules about that structure.
For example, parentheses have to come in matching pairs, so (1 + 2) is legal,
but 8) is a syntax error.

Question 24

semantic error

Answer 24

The third type of error is “semantic”, which means related to meaning.
If there is a semantic error in your program, it will run without generating error
messages, but it will not do the right thing. It will do something else. Specifically, it
will do what you told it to do.

Question 25

runtime error

Answer 25

The second type of error is a runtime error, so called because the error does
not appear until after the program has started running. These errors are also called
exceptions because they usually indicate that something exceptional (and bad) has
happened.

Question 26

variable

Answer 26

name that refers to a value

Question 27

assignment

Answer 27

statement that assigns to a variable

Question 28

keyword

Answer 28

A reserved word that is used to parse a program; you cannot use keywords like
if, def, and while as variable names.

Question 29

statement

Answer 29

A section of code that represents a command or action. So far, the statements
we have seen are assignments and print statements.

Question 30

concatenate

Answer 30

: To join two operands end-to-end.

Question 31

argument

Answer 31

expression in parenthesis of a function call
function(argument)
print('hello world')

Question 32

function

Answer 32

It is common to say that a function “takes” an argument and “returns” a result. The result
is also called the return value.

Question 33

module

Answer 33

a file that contains a collection of related functions.

import some module

Question 34

to call on a function in amodule

Answer 34

To access
one of the functions, you have to specify the name of the module and the name of the
function, separated by a dot (also known as a period). This format is called dot notation.
»> ratio = signal_power / noise_power
»> decibels = 10 * math.log10(ratio)
»> radians = 0.7
»> height = math.sin(radians)
The first example uses math.log10 to compute a signal-to-noise ratio in decibels (assuming
that signal_power and noise_power are defined). The math module also provides log,
which computes logarithms base e.

Question 35

function definition

Answer 35

specifies the name of a new function and the
sequence of statements that run when the function is called.
Here is an example:
def print_lyrics():
print("I'm a lumberjack, and I'm okay.")
print("I sleep all night and I work all day.")

Question 36

paramaters

Answer 36

parameter is a variable in a method definition. When a method is called, the arguments are the data you pass into the method’s parameters. Parameter is variable in the declaration of function.
equivalent to argument

Question 37

local variables

Answer 37

When you create a variable inside a function, it is local, which means that it only exists
inside the function.

Question 38

function call

Answer 38

statement that runs the functions

Question 39

void function

Answer 39

always returns ‘none’

Question 40

dot notation

Answer 40

The syntax for calling a function in another module by specifying the module
name followed by a dot (period) and the function name.

Question 41

docstring

Answer 41

string at the beginning of a function that explains the interface (“doc” is
short for “documentation”)

””” “””

Question 42

‘for’ statement

Answer 42

The syntax of a for statement is similar to a function definition. It has a header that ends
with a colon and an indented body. The body can contain any number of statements.
A for statement is also called a loop because the flow of execution runs through the body
and then loops back to the top. In this case, it runs the body four times.

Question 43

encapsulation ** need help

Answer 43

An objects variables should not always be directly accessible.

To prevent accidental change, an objects variables can sometimes only be changed with an objects methods. Those type of variables are private variables.

The methods can ensure the correct values are set. If an incorrect value is set, the method can return an error.

Question 44

interface

Answer 44

what user deals with.

An interface is “clean” if it allows the
caller to do what they want without dealing with unnecessary details.

Question 45

refactoring

Answer 45

rearranging a program to improve interfaces and facilitate code re-use

Question 46

generalization

Answer 46

The process of replacing something unnecessarily specific (like a number)
with something appropriately general (like a variable or parameter).

Question 47

precondition

Answer 47

A requirement that should be satisfied by the caller before a function starts.

Question 48

floor division operator

Answer 48

//
divides two numbers and rounds down to an integer

Question 49

modulus operator

Answer 49

%

divides two numbers and returns remainder… often used with //

Question 50

1) x % 10

2) x % 100

Answer 50

1) finds right most digit of x

2) finds the two right most digits of x

Question 51

boolean expressions

Answer 51

expression that is either true or false

true and false are bool type objects

Question 52

relational operators

Answer 52

x == y #x is equal in value to y
x != y # x is not equal to y
x > y # x is greater than y
x < y # x is less than y
x >= y # x is greater than or equal to y
x <= y # x is less than or equal to y

Question 53

logical operators

Answer 53

and, or, not

Question 54

conditional statements

Answer 54

to say to do something only if a condition meets certain criteria

if ____:
do something

Question 55

if else statements

Answer 55

if x % 2 == 0:
print(‘x is even’)
else:
print(‘x is odd’)

Question 56

chained conditionals

Answer 56

if elif else
if x < y:
print(‘x is less than y’)
elif x > y:
print(‘x is greater than y’)
else:
print(‘x and y are equal’)
elif is an abbreviation of “else if”. Again, exactly one branch will run. There is no limit on
the number of elif statements. If there is an else clause, it has to be at the end, but there
doesn’t have to be one.
if choice == ‘a’:
draw_a()
elif choice == ‘b’:
draw_b()
elif choice == ‘c’:
draw_c()
Each condition is checked in order. If the first is false, the next is checked, and so on. If one
of them is true, the corresponding branch runs and the statement ends. Even if more than
one condition is true, only the first true branch runs.

Question 57

nested conditionals

Answer 57

One conditional can also be nested within another. We could have written the example in
the previous section like this:
if x == y:
print('x and y are equal')
else:
if x < y:
print('x is less than y')
else:
print('x is greater than y')

Question 58

recursive function

Answer 58

one function calls another, or even calls itself
def countdown(n):
if n <= 0:
print(‘Blastoff!’)
else:
print(n)
countdown(n-1)
If n is 0 or negative, it outputs the word, “Blastoff!” Otherwise, it outputs n and then calls
a function named countdown—itself—passing n-1 as an argument.

Question 59

fibonacci

Answer 59

After factorial, the most common example of a recursively defined mathematical function
is fibonacci:
fib(0)=0
fib(1) =1
fibonacci(n) = fibonacci(n − 1) + fibonacci(n − 2)

Question 60

temporary variable

Answer 60

A variable used to store an intermediate value in a complex calculation.

Question 61

dead code

Answer 61

Part of a program that can never run, often because it appears after a return
statement

Question 62

reassignment

Answer 62

A new assignment makes an existing variable refer to a new value (and stop
referring to the old value).
>>> x = 5
>>> x
5
>>> x = 7
>>> x
7

Question 63

iteration

Answer 63

repetition of an identical or similar task

for loops/ while statements

Question 64

while statement

Answer 64

More formally, here is the flow of execution for a while statement:

1. Determine whether the condition is true or false.
2. If false, exit the while statement and continue execution at the next statement.
3. If the condition is true, run the body and then go back to step 1.

def countdown(n):
while n > 0:
print(n)
n = n - 1
print('Blastoff!')

Question 65

index

Answer 65

expression in brackets. indicates which character in the sequence you want.
>>> fruit = 'banana'
>>> letter = fruit[1]
>>> letter
'a'

Question 66

len

Answer 66

> > > fruit = ‘banana’
len(fruit)
6

Question 67

slice

Answer 67

A segment of a string is called a slice. Selecting a slice is similar to selecting a character:
>>> s = 'Monty Python'
>>> s[0:5]
'Monty'
>>> s[6:12]
'Python'
The slice operator also works on lists:
92 Chapter 10. Lists
>>> t = ['a', 'b', 'c', 'd', 'e', 'f']
>>> t[1:3]
['b', 'c']
>>> t[:4]
['a', 'b', 'c', 'd']
>>> t[3:]
['d', 'e', 'f']

Question 68

immutable

Answer 68

cannot be changed after its created

Question 69

mutable

Answer 69

a mutable object can be changed after it is created

Question 70

immutable strings

Answer 70

The reason for the error is that strings are immutable, which means you can’t change an
existing string. The best you can do is create a new string that is a variation on the original:
»> greeting = ‘Hello, world!’
»> new_greeting = ‘J’ + greeting[1:]
»> new_greeting
‘Jello, world!’
This example concatenates a new first letter onto a slice of greeting. It has no effect on the
original string

Question 71

counting

Answer 71

word = ‘banana’
count = 0
for letter in word:
if letter == ‘a’:
count = count + 1
print(count)
This program demonstrates another pattern of computation called a counter. The variable
count is initialized to 0 and then incremented each time an a is found. When the loop exits,
count contains the result—the total number of a’s.

Question 72

‘in’ operator

Answer 72

The word in is a boolean operator that takes two strings and returns True if the first appears
as a substring in the second:
>>> 'a' in 'banana'
True
>>> 'seed' in 'banana'
False

Question 73

list

Answer 73

a list is a sequence of values. In a string, the values are characters; in a list,
they can be any type. The values in a list are called elements or sometimes items.
The elements
of a list don’t have to be the same type. The following list contains a string, a float, an
integer, and (lo!) another list:
[‘spam’, 2.0, 5, [10, 20]]

Question 74

nested list

Answer 74

list within another list

Question 75

mutable lists

Answer 75

Unlike strings, lists are mutable. When the bracket operator appears on the left side of an
assignment, it identifies the element of the list that will be assigned.
»> numbers = [42, 123]
»> numbers[1] = 5
»> numbers
[42, 5]
The one-eth element of numbers, which used to be 123, is now 5.

Question 76

list operations

Answer 76

The + operator concatenates lists:
>>> a = [1, 2, 3]
>>> b = [4, 5, 6]
>>> c = a + b
>>> c
[1, 2, 3, 4, 5, 6]
The * operator repeats a list a given number of times:
>>> [0] * 4
[0, 0, 0, 0]
>>> [1, 2, 3] * 3
[1, 2, 3, 1, 2, 3, 1, 2, 3]
The first example repeats [0] four times. The second example repeats the list [1, 2, 3]
three times.

Question 77

list.append

Answer 77

append adds a new element
to the end of a list:
>>> t = ['a', 'b', 'c']
>>> t.append('d')
>>> t
['a', 'b', 'c', 'd']

Question 78

list.extend

Answer 78

extend takes a list as an argument and appends all of the elements:
>>> t1 = ['a', 'b', 'c']
>>> t2 = ['d', 'e']
>>> t1.extend(t2)
>>> t1
['a', 'b', 'c', 'd', 'e']
This example leaves t2 unmodified.

Question 79

list.sort

Answer 79

sort arranges the elements of the list from low to high:
»> t = [‘d’, ‘c’, ‘e’, ‘b’, ‘a’]
»> t.sort()
»> t
[‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
Most list methods are void; they modify the list and return None.

Question 80

add up everything in a list

Answer 80

To add up all the numbers in a list, you can use a loop like this:
def add_all(t):
total = 0
for x in t:
total += x
return total

Question 81

deleting elements from lists

Answer 81

you can use pop:
>>> t = ['a', 'b', 'c']
>>> x = t.pop(1)
>>> t
['a', 'c']
>>> x
'b'
pop modifies the list and returns the element that was removed. If you don’t provide an
index, it deletes and returns the last element.
If you don’t need the removed value, you can use the del operator:
>>> t = ['a', 'b', 'c']
>>> del t[1]
>>> t
['a', 'c']
If you know the element you want to remove (but not the index), you can use remove:
>>> t = ['a', 'b', 'c']
>>> t.remove('b')
>>> t
['a', 'c']
The return value from remove is None.
To remove more than one element, you can use del with a slice index:
>>> t = ['a', 'b', 'c', 'd', 'e', 'f']
>>> del t[1:5]
>>> t
['a', 'f']
As usual, the slice selects all the elements up to but not including the second index.

Question 82

convert string to list of characters

Answer 82

> > > s = ‘spam’
t = list(s)
t
[’s’, ‘p’, ‘a’, ‘m’]

Question 83

Aliasing

Answer 83

If a refers to an object and you assign b = a, then both variables refer to the same object:
>>> a = [1, 2, 3]
>>> b = a
>>> b is a
True

An object with more than one reference has more than one name, so we say that the object is aliased.
if the aliased object is mutable, changes named to one will affect the other

Question 84

editing strings vs lists

Answer 84

Most list methods modify the argument and return None. This is the opposite of the
string methods, which return a new string and leave the original alone.

Question 85

equivalent vs identical

Answer 85

equivalent: Having the same value.
identical: Being the same object (which implies equivalence).

Question 86

reference

Answer 86

association between a variable and its value

Question 87

dictionary

Answer 87

A dictionary is like a list, but more general. In a list, the indices have to be integers; in a dictionary they can be (almost) any type. A dictionary contains a collection of indices, which are called keys, and a collection of values. Each key is associated with a single value. The association of a key and a value is called a key-value pair or sometimes an item. in mathematical language, a dictionary represents a mapping from keys to values, so you can also say that each key “maps to” a value. As an example, we’ll build a dictionary that
maps from English to Spanish words, so the keys and the values are all strings

Question 88

{ }

Answer 88

> > > eng2sp = dict()
eng2sp
{}
eng2sp = {‘one’: ‘uno’, ‘two’: ‘dos’, ‘three’: ‘tres’}
The squiggly-brackets, {}, represent an empty dictionary. To add items to the dictionary, you can use square brackets:
eng2sp[‘one’] = ‘uno’
This line creates an item that maps from the key ‘one’ to the value ‘uno’. If we print the
dictionary again, we see a key-value pair with a colon between the key and value:
eng2sp
{‘one’: ‘uno’}

Question 89

dictionary mapping

Answer 89

The order of the key-value pairs might not be the same. If you type the same example
on your computer, you might get a different result. In general, the order of items in a
dictionary is unpredictable.
But that’s not a problem because the elements of a dictionary are never indexed with integer
indices. Instead, you use the keys to look up the corresponding values:
»> eng2sp[‘two’]
‘dos’
The key ‘two’ always maps to the value ‘dos’ so the order of the items doesn’t matter

Question 90

how to lookup a value in a dictionary

Answer 90

Given a dictionary d and a key k, it is easy to find the corresponding value v = d[k]

Question 91

tuple

Answer 91

A tuple is a sequence of values. The values can be any type, and they are indexed by
integers, so in that respect tuples are a lot like lists. The important difference is that tuples are immutable.
Syntactically, a tuple is a comma-separated list of values:
»> t = ‘a’, ‘b’, ‘c’, ‘d’, ‘e’
To create a tuple with a single element, you have to include a final comma:
»> t1 = ‘a’,
»> type(t1)

Question 92

tuples=immutable

Answer 92

But if you try to modify one of the elements of the tuple, you get an error:
»> t[0] = ‘A’
TypeError: object doesn’t support item assignment
Because tuples are immutable, you can’t modify the elements. But you can replace one
tuple with another:
»> t = (‘A’,) + t[1:]
»> t
(‘A’, ‘b’, ‘c’, ‘d’, ‘e’)
This statement makes a new tuple and then makes t refer to it.

Question 93

list comprehension

Answer 93

def capitalize_all(t):
res = []
for s in t:
res.append(s.capitalize())
return res
We can write this more concisely using a list comprehension:
def capitalize_all(t):
return [s.capitalize() for s in t]
The bracket operators indicate that we are constructing a new list. The expression inside
the brackets specifies the elements of the list, and the for clause indicates what sequence
we are traversing.

Question 94

Generator expression

Answer 94

Generator expressions are similar to list comprehensions, but with parentheses instead of
square brackets:
»> g = (x**2 for x in range(5))
»> g
at 0x7f4c45a786c0>
The result is a generator object that knows how to iterate through a sequence of values. But
unlike a list comprehension, it does not compute the values all at once; it waits to be asked.
The built-in function next gets the next value from the generator:
»> next(g)
0
»> next(g)
1