Python Moodle

Question 1

What is an algorithm?

Answer 1

A step by step sequence of instructions that if followed exactly will solve the problem under consideration.
Algorithms are like recipes: they must be followed exactly, they must be clear and unambiguous, and they must end.

Question 2

What is a program?

Answer 2

A sequence of instructions that specifies how to perform a computation.

Question 3

The differences between natural and formal languages include:

Answer 3

ambiguity, redundancy, and literalness

Question 4

Source code is another name for:

Answer 4

the instrucions in a program, written in a high-level language.

Question 5

What is the difference between a high-level programming language and a low-level programming language?

Answer 5

It is high-level if the program must be processed before it can run, and low-level if the computer can execute it without additional processing.

Question 6

What is the difference between a compiler and interpreter?

Answer 6

Interpreter reads a high-level program line by line and performs computations.

A compiler reads the high-level program (soucre code) and translates it into object code. The object code is then executed without further translation.

Interpreter: line by line translation
Compiler: translates the whole book

Question 7

What is debugging?

Answer 7

tracking down programming errors and correcting them

Question 8

What type of errors extist and explain?

Answer 8

1. Syntax Error
   syntax = structure of the program
   Syntax errors are mistakes in using the language. Examples of syntax errors are missing a comma or a quotation mark, or misspelling a word. This is typically found by the compiler/interpreter.
2. Runtime Error (=excpection)
   Runtime, or execution-time, errors are found when a script or function is executing (=found by the interpreter). Ex. divide by 0.
3. Semantic Error (=logical error)
   semantic = meaning of a program
   A semantic error is a mistake in reasoning by the programmer, but it is not a mistake in the programming language (=can only be found by the programmer)

Question 9

What is a token?

Answer 9

One of the basic elements of the syntactic structure of a program, analogous to a word in a natural language.

Question 10

Python is a

Answer 10

• general-purpose programming language
• scripting language
• interpreted language

Question 11

What is the order of the program execution process?

Answer 11

1. Write the code
2. Compile
3. Debug
4. Execute the compiled and debugged code

Question 12

In a nutshell what are the key components of a computer program?

Answer 12

Input
Operations
Control Structures
Ouput

Question 13

What is the truncated division operator?

Answer 13

ex. 9//5 = 1
–> ignores the remainder

Question 14

What is the modulus operator?

Answer 14

ex. 7 % 3 = 1
1 % 5 = 1 (5*0 + 1)
–> keeps only the remainder

Question 15

What are keywords?

Answer 15

Keywords define the language’s syntax rules and structure, and they cannot be used as variable names,
e.g. and, def, class, True, try, except, global

Question 16

What is increment, bumping, and decrement?

Answer 16

increment: adding something to a variable
bumping: increment a variable by 1 ( x+= 1)
decrement: subtracting something to a variable

Question 17

What to watch out for when using the input function?

Answer 17

Input function returns a string value

Question 18

What to watch out for when choosing a variable name?

Answer 18

• begin with a letter
• no illigeal characters (+,$,..)
• no keywords

Question 19

Write the Python code that displays the value of a,b,c in one line with the ‘+’ operator:

a = int(input(“please enter a number”))
b = input(“please enter a sentence”)
c = ‘the input sentence is: ‘

Answer 19

In order to use the + first, we have to make sure that all the variables have the same data type.

The value of b and c is a string but the value of a is an integer so we need to convert it to a string by using str().

print(str(a) + b + c)

Question 20

Important difference between string and list?

Answer 20

Lists can be changed while strings are immutable.

Question 21

How do we call a string that contains no characters?

Answer 21

empty string

Question 22

What is the difference between lists and tuples?

Answer 22

lists:
[10, 20, 30, 40]
[“spam”, “bungee”, “swallow”]
mutable

tuples:
julia = (“Julia”, “Roberts”, 1967, “Duplicity”, 2009, “Actress”, “Atlanta, Georgia”)
immutable

Question 23

How do you access the last character or middle character of the string fruit = “grape”?

Answer 23

lastchar = fruit[-1]
lastchar = fruit[len(fruit) - 1]

midchar = fruit[len(fruit) // 2]

Question 24

What is a slice operator?

Answer 24

The slice operator [n:m] returns the part of the string starting with the character at index n and go up to but not including the character at index m.

Question 25

What does the ‘+’ operator and ‘*’ operator do with lists?

fruit = [“apple”,”orange”,”banana”,”cherry”]
print([1,2] + [3,4])
print(fruit+[6,7,8,9])
print([0] * 4)

Answer 25

+ concatenate
* repeats items in a list

[1, 2, 3, 4]
[‘apple’, ‘orange’, ‘banana’, ‘cherry’, 6, 7, 8, 9]
[0, 0, 0, 0]

Beware when adding different types together! Python doesn’t understand how to concatenate different types together. Thus, if we try to add a string to a list with [‘first’] + “second” then the interpreter will return an error.

Question 26

What does the count method do?

a = “I have had an apple on my desk before!”
print(a.count(“e”))
———————
z = [‘atoms’, 4, ‘neutron’, 6, ‘proton’, 4, ‘electron’, 4, ‘electron’, ‘atoms’]
print(z.count(“4”))
print(z.count(4))
print(z.count(“a”))
print(z[0].count(“a”))
print(z.count(“electron”))

Answer 26

It requires that you provide one argument, which you would like to count. The method then returns the number of times that the argument occurred in the string/list the method was used on

5
———————
0
3
0
1
2

Question 27

What does the index method do?

music = “Pull out your music and dancing can begin”
bio = [“Metatarsal”, “Metatarsal”, “Fibula”, [], “Tibia”, “Tibia”, 43, “Femur”, “Occipital”, “Metatarsal”]

print(music.index(“m”))
print(music.index(“your”))

print(bio.index(“Metatarsal”))
print(bio.index([]))
print(bio.index(43))

Answer 27

The other method that can be helpful for both strings and lists is the index method. The index method requires one argument, and, like the count method, it takes only strings when index is used on strings, and any type when it is used on lists. For both strings and lists, index returns the leftmost index where the argument is found. If it is unable to find the argument in the string or list, then an error will occur.

14
9
0
3

Question 28

song = “The rain in Spain…”
wds = song.split()
print(wds)
———————
song = “The rain in Spain…”
wds = song.split(‘ai’)
print(wds)

Answer 28

The split method breaks a string into a list of words.

[‘The’, ‘rain’, ‘in’, ‘Spain…’]

[‘The r’, ‘n in Sp’, ‘n…’]

Question 29

wds = [“red”, “blue”, “green”]
glue = ‘;’
s = glue.join(wds)
print(s)
print(wds)

print(“***“.join(wds))
print(““.join(wds))

Answer 29

red;blue;green
[‘red’, ‘blue’, ‘green’]
redbluegreen
redbluegreen

Question 30

What is printed by the following statements?

s = “python rocks”
print(len(s))

Answer 30

12 –> whitespace is a character

Question 31

What is printed by the following statements?

L = [0.34, ‘6’, ‘SI106’, ‘Python’, -2]
print(len(L[1:-1]))

Answer 31

3
[n:m] –> n wird mitgezählt, m nicht

Question 32

What will be stored in the variable ty below?

qu = “wow, welcome week!”
ty = qu.index(“we”)

Answer 32

5

When we get the index of a string that is longer than one character, we get the index for the first character in the string.

Question 33

What will be stored in the variable ty below?

qu = “wow, welcome week! Were you wanting to go?”
ty = qu.count(“we”)

Answer 33

2

There is a difference between “we” and “We” which means there are only two in the string –> case sensitive

Question 34

What is the ouput of this code?

for achar in “Go Spot Go”:
print(achar)

Answer 34

G
o

S
p
o
t

G
o

Question 35

What is the range function range(n)?

ex. range(3)

Answer 35

starts at 0 and goes up to but not including n.

range(3) –> [0,1,2]

Question 36

When is the for variable _ used?

for _ in range(3):
print(“This line will execute three times”)
print(“This line will also execute three times”)

Answer 36

When we don’t intend to ever refer to the loop variable

Question 37

How many comparison operators exist in Python?

Answer 37

6
x == y
x != y
x > y
x < y
x >= y
x <= y

Question 38

What does the ‘in’ operator?

Answer 38

The in operator tests if one string is a substring of another:

print(‘p’ in ‘apple’)
print(‘i’ in ‘apple’)
print(‘’ in ‘a’)
print(‘’ in ‘apple’)

True
False
True
True

Question 39

What is the type of m?

l = [‘w’, ‘7’, 0, 9]
m = l[1:2]

Answer 39

It’s a list! A slice returns a list no matter how large the slice size is.

Question 40

What is the type of m?

l = [‘w’, ‘7’, 0, 9]
m = l[1]

Answer 40

It’s a string! [1] indicates it is the second element ‘7’ in the list, and the quotes around the number mean that this is a string.

Question 41

What is the type of a?

b = “My, what a lovely day”
x = b.split(‘,’)
z = ““.join(x)
y = z.split()
a = ““.join(y)

Answer 41

It’s a string!

The string is split into a list, then joined back into a string, then split again, and finally joined back into a string “Mywhatalovelyday”.

Question 42

What is the output message of the following code:

x,y,z = 1,2,3

def sum_two(x,y,z):
return x+y, y+z, x+z

result = sum_two(x,y,z)

a,b = result[::2]

print(str(a) +str(b))

Answer 42

34

Yes, result = (3,5,4) after calling sum_two function. a, b = (3,4) after executing result[::2]. Finally it concatenates ‘3’ and ‘4’.

result[::2] –> anfang bis ende in 2er Schritten
element 0, 2, 4, … –> a,b = (3,4)

Question 43

Array-based structure vs. linked-based structure:

Which data structure is better?

Answer 43

1. The array-based structure generally takes less memory as compared to the linked-based structure if the collection is considered relatively full.
2. The array-based structure is preferred if the total number of elements of a collection can be predetermined at the start of the program implementation.
3. The linked-based structure is preferred if adding new elements and removing existing elements are regularly performed at random positions; although the array-based structure is more efficient for accessing elements at random.

Question 44

Which of the following can be used in Python? There are multiple answers for this question.

primitive data types
abstract data types
user-defined data types
predefined data types
all of the above

Answer 44

primitive data types
abstract data types
user-defined data types

Question 45

Abstract data type is the built-in data type in Python. True or false?

Answer 45

False, primitive data types is the built-in data type.

Question 46

What is an example for aliasing?

Answer 46

a = [81, 82, 83]
b = a
print(a is b)
——-
True

Since variables refer to objects, if we assign one variable to another, both variables refer to the same object. In general, it is safer to avoid aliasing when you are working with mutable objects.

Question 47

What does the ‘is’ operator?

Answer 47

We can test whether two names refer to the same object.

Question 48

When is it useful to use cloning lists?

Answer 48

If we want to modify a list and also keep a copy of the original, we need to be able to make a copy of the list itself, not just the reference.

a = [81,82,83]

b = a[:] # make a clone using slice
print(a == b)
print(a is b)

b[0] = 5

print(a)
print(b)

Question 49

What is printed by the following statements:

s = “Ball”
s[0] = “C”
print(s)

Answer 49

Error, strings are immutable.

Question 50

What is printed by the following statements?

alist = [4,2,8,6,5]
blist = alist * 2
blist[3] = 999
print(alist)
[4,2,8,999,5,4,2,8,6,5]
[4,2,8,999,5]
[4,2,8,6,5]

Answer 50

[4,2,8,6,5]

Question 51

What is printed by the following statements?

alist = [4,2,8,6,5]
alist = alist + 999
print(alist)

Answer 51

Error, you cannot concatenate a list with an integer.

Question 52

What is printed by the following statements?

s = “python rocks”
print(s.count(“o”) + s.count(“p”))

Answer 52

3

Question 53

What is printed by the following statements?

s = “python rocks”
print(s[1]*s.index(“n”))

Answer 53

yyyyy

Question 54

What is printed by the following statements?

v = 2.34567
print(‘ {:.2f} {:.7f}’.format(v, v, v))

Answer 54

2.3 2.35 2.3456700

Question 55

What are simple/atomic data types?

Answer 55

The represented data values cannot be further decomposed, e.g. int, float, bool

Question 56

What are complex data types?

Answer 56

We have complex data types for representing collections of multiple data values, e.g. strings, lists, tuples, dictionaries, and sets.

Question 57

What is an array-based structure?

Answer 57

• Array is a collection of data items organised and stored sequentially
• Store collection of data items of the same type
• Each data item can be randomly accessed using the concept of ‘indexing’
• Has a fixed size
• Is costly to Inserting new data items

Question 58

What is a linked-based structure?

Answer 58

• Linked list is a collection of nodes where each node has two parts: 1. data and 2.
  Referencer to the next node
• The data items are linked together as a collection using the concept of ‘referencing’.
• Each data item can be accessed sequentially starting from the first data items
• Has a dynamic size
• No random access
• Extra memory space for reference

Question 59

What are dictionary methods you have learned in class?

Answer 59

x.keys() –> returns a view of the keys in the dictionary

x.values() –> returns a view of the values in the dictionary

inventory = {‘apples’: 430, ‘bananas’: 312, ‘oranges’: 525, ‘pears’: 217}

for k, v in inventory.items():
print(“Got”, k, “that maps to”, v)
————–

x.get(key) or x.get(key,alt) –> returns the value associated with key none or alt otherwise

Question 60

As dictionaries are mutable what porblem can arise?

Answer 60

You need to be aware of aliasing!

opposites = {‘up’: ‘down’, ‘right’: ‘wrong’, ‘true’: ‘false’}
alias = opposites

print(alias is opposites)

alias[‘right’] = ‘left’
print(opposites[‘right’])
————–
True
left

Question 61

What are ‘sets’?

Answer 61

A set is a collection of unique, unordered items. Essentially, it is a list where there are no repeating elements.

a_set = set([1,2,3,3,4,5,2,2,2])
print(a_set)
————–
{1, 2, 3, 4, 5}

Question 62

How can you manipulate sets?

Answer 62

add(item), remove(item) (=discard(item) but no runtime error if item is not present)

pop() –> remove random item fromm set

clear() –> makes set empty

Question 63

What is printed by the following statements?

mydict = {“cat”:12, “dog”:6, “elephant”:23, “bear”:20}
print(23 in mydict)

Answer 63

False, the in operator returns True if a key is in the dictionary, False otherwise.

Question 64

What are class and instance variables?

Answer 64

For a class, variables defined outside the body of any methods are called class attributes –> global, can be accessed inside or outside of the classing using the dot operator.

Instance variables are unique to each instance of a class and they are defined with the self.keyword

Question 65

Which of these is not the fundamental concept of OOP?

• abstraction
• encapsulation
• inheritance
• polymophism
• instantiation

Answer 65

instantiation

Question 66

Encapsulation vs. Abstraction

Answer 66

• Hiding data complexity
• Encapsulation means storing the code of each functionality in one place. While abstraction is responsible for presenting only non-sensitive information to the user by hiding the sensitive information.

Question 67

What is scoping?

Answer 67

Define the part of the program where a variable is accessible

Question 68

What is lifetime?

Answer 68

Define the duration for which a variable exists during the program execution

Question 69

What is a global variable?

Answer 69

Can be accessed throughout the entire program

Exists until the execution of the program terminated

Question 70

What is a locla variable?

Answer 70

Can only be accessed within the function it was defined

Exists until the function exists

Question 71

How many objects and reference variables are there for the given Python code?

class A:
print(“Inside class”)
A()
A()
obj=A()

Answer 71

3 objects, 1 reference variable

obj is the reference variable here and an object will be created each time A() is called.So there will be 3 objects created. Run the following code to see

Question 72

Which of the following is correct with respect to OOP concept in Python?

Objects are real world entities while classes are not real.

Classes are real world entities while objects are not real.

Both objects and classes are real world entities.

Both object and classes are not real.

Answer 72

Objects are real world entities while classes are not real.

In OOP, classes are basically the blueprint of the objects. They don’t have physical existence.

Question 73

What will be the output of the below Python code?

class A:

def \_\_init\_\_(self,num):

    num=3

    self.num=num

def change(self):

    self.num=7

a=A(5)

print(a.num)

a.change()

print(a.num)

Answer 73

3
7

Question 74

In python, what is the method inside class?

Answer 74

In OOP of Python, function is known by “method”.

Question 75

Which of the following is correct?
class A:

def \_\_init\_\_(self):

    self.count=5

    self.count=count+1

a=A()
print(a.count)

5
6
0
Error

Answer 75

It will throw an error as inside constructor, “count” is not defined.

Question 76

What does super() in OOP?

Answer 76

Super() will call every parent’s version of the function

Question 77

What is Stack ADT?

Answer 77

stack abstruct data type is an ordered collection where data items are accessed based on LIFO (last-In-First-Out)

push(item): add a new item onto the top of the stack

pop(): remove an existing item from the top of the stack

peek(): look at the top item of the stack; without modifying the stack

Question 78

What is Queue ADT?

Answer 78

• An ordered collection where data items are accessed based on FIFO (First-In-First-Out)
• adding new items at the “rear” of the queue
• Removing existing items at the “head” of the queue

append(item)/Enqueue(): append a new item at the rear (end) of the queue
serve()/Dequeue(): remove an existing item from the front of the queue

Question 79

What is self in classes?

Answer 79

self is a variable referencing to the instance itself, when we create an instance of the Class.

The variables with prefix “self.” are called instance variables. The values are attached to the instance rather than the Class.

self is always put as the first argument when we define a Class method.

And of course, self is just a name. You can change it to other names, although it is not preferred.

Question 80

When a child class inherits from only one parent class, it is called?

Answer 80

When a child class inherits from only one parent class, it is called single inheritance.

Question 81

What does the built-in function type do in the context of classes?

Answer 81

Determines the class name of any value.

For example:&raquo_space;> help() usually gives information of the class on any built-in type or function.

Question 82

The child’s __init__() function overrides the inheritance of the parent’s __init__() function. True or False?

Answer 82

True!
The child’s __init__() function overrides the inheritance of the parent’s __init__() function.

Question 83

Which function makes the child class inherit all the methods and properties from its parent?

Answer 83

super () will make the child class inherit all the methods and properties from its parent

Question 84

Which inheritance is a blend of more than one type of inheritance?

Answer 84

Hybrid inheritance: This form combines more than one form of inheritance.

Question 85

What are available mode to open a file in Python?

Answer 85

r: open for reading
w: open for writing, tuncating the file first
x: open for exclusive creation, failing if the file already exists
a: open for writing, appending to the end of the file if it exists
b: binary mode (e.g. images, videos)
t: text mode
+: open for updating

Question 86

In which modes is readlines() not available?

Answer 86

With mode ‘w’ and ‘a’

Question 87

What is the problem?

with open(‘ingredients’, ‘r’) f:
i = f.readlines()
for l in lines:
print(l.split(‘\t’)[0])
f.close()

Answer 87

i is a list. It does not have split() method.

Question 88

Name the three most common types of test cases:

Answer 88

• valid cases
• invalid cases
• boundary cases.

Question 89

Name 4 error messages in Python

Answer 89

SyntaxError:
error in the syntax, e.g. ‘:’

NameError:
try to use a value before initialising it or you attempt to use a package without first importing it

TypeError:
try to use incompatible data types within a single statement or passing arguments of the wrong type to a function, e.g. adding a string and an integer or passsing a list to a function that expacts an integer

ValueError:
function receives an argument with the correct data type but with an inappropriate value.
e.g. negative number in .sqrt()

Question 90

What is unittest?

Answer 90

unittest is a package to automate testing

Question 91

Why is testing important?

Answer 91

• fixing a bug early is way cheaper in earlier stages
• ensure correctness –> program has to work properly (and humans make mistakes)
• to ensure the quality of our program is high –> stay competitive

Question 92

Working with file read/write:

inputFile.readline()
for line in inputFile
inputFile.readlines()
inputFile.read()

Answer 92

read one line at a time (‘\n’ is included) until the end of the file is reached

iterate through each of the lines on each iteration of the loop

read the entire content of a file and return it as a list

read the entire content of a file and return it as a string

Question 93

Name 4 levels of testing:

Answer 93

Unit testing:
- Individual units or components of a program are tested
- Validate that each unit is fully functional without errors

Integration testing:
- Individual units are combined and tested as a group
- Errors/defects might expose during the interaction between integrated units

System testing:
- The complete integrated application is tested as a whole
- Ensure that all the functionality and requirements are achieved

Acceptance testing:
- The complete application is tested by users before its deployment
- Evaluate the system complies with all the business requirements

Question 94

How is testing performed?

Explain basic vs. good testing strategy

Answer 94

Basic approach:
- Define a test strategy with various test cases identified, which are important to ensure the correctness of your program

Good testing strategy
- Make sure all the functionality can be covered/tested in a finite amount of testing time
- Composed of a reasonable and manageable number of test cases
- Maximise the chance of detecting an error or a defect

Question 95

What does assertEqual check?

Answer 95

check if a==b

assertEqual(first, second, msg=None)

Question 96

Assign SyntaxError, NameError, TypeError, and ValueError to the following codes:

1. if a_number > 2
   print(a_number, “is greater than 2”)

2.
a_number = random.random()

3.
if a_number > 2:
print(a_number + “is greater than 2”)

4.
sum_of_two = int(‘1’) + int(‘b’)

Answer 96

SyntaxError –> missing ‘:’
NameError –> using random.random() before importing library random
TypeError –> concatenate int with string
ValueError –> passing a wrong value to a function, here string ‘b’ to int()

Question 97

Which of the following exception will be thrown for the given program?

def test_function(first_arg, second_arg):
result = first_arg + second_arg
return result

print(test_function(‘1’,2))

Answer 97

result = string + int –> TypeError

Question 98

Which of the following exception will be thrown for the given program?

NameError, AttributeError, RuntimeError, None of the above

class Point:
def __init__(self, x=0, y=0):
self.x = x
self.y = y

def get_x(self):
    return self.x
    
def get_y(self):
    return self.y a_point = Point(1,2) a_point.set_x(2)

Answer 98

.set_x() doesn’t exist –> AttributeError

Question 99

Which block lets you test a block of code for errors?

try
except
finally
none of the above

Answer 99

try

Question 100

It is raised when the requested module definition is not found.
Import Error

Import Error
EOF Error
Index Error
Type Error

Answer 100

Import Error

Question 101

What will be the output for the following code?

try:
print(x)
except:
print(““An exception occurred””)

Answer 101

An exception occurred be the output for the followinng code because the try block will generate an error, because x is not defined.

Question 102

What will be the output for the What will be the output for the following code?

x=10
y=8
assert x>y, ‘X too small’

Answer 102

No ouput.

assert x>y returns True and no other print ouput –> no ouput

if x<y output would print “X too small”

Question 103

Which exception is raised when a calculation exceeds the maximum limit for a numeric type?
StandardError
ArithmeticError
OverflowError
FloatingPointError

Answer 103

OverflowError : Raised when a calculation exceeds maximum limit for a numeric type

Question 103

What returns
random.random()
random.randint(a,b)
random.choice()

?

Answer 103

random.random():
Return a random floating number btw 0 and 1

random.randint(a,b):
Return a random number between and including a and b

random.choice(): Return a random element from a list

Question 103

What is re (Regular Expression)?

Answer 103

The Regular Expression (re or regex) is a string matching module that allows finding the specified pattern in the given string/text. For example, we have a very long text of 500 lines, and we want to find all the words that start with the character “P” and end with the symbol “N” it can be done using the regex.

Question 104

What does re.findall(pattern, text)?

Answer 104

The findall function works similarly to the search function, and the advantage is it finds all the matching and return the list of string or tuples.

Question 105

What does re.sub(pattern, replace_word, text)?

Answer 105

The sub-function finds and substitutes the pattern with a new given the word in the text. So, first, it searches and then does the substitution.

import re

text = “Python is fun. Python is fast, easy to learn, and awesome.”
pattern = r”Python”
replace_word = “python”

python is fun. python is fast, easy to learn, and awesome.

Question 106

What does pattern = r”[Pp].*?[nN]”?

Answer 106

’.*?’: it tries to match any number of characters and stops when the next character in the regex is found

Question 107

In a regular expression, the pattern “\w” is equivalent to:

Answer 107

Matches any alphanumeric character; this is equivalent to the class [a-zA-Z0-9_].

Question 108

Consider the following code:

import numpy as np
a = np.arange(0,20,2)
a.shape = (2,5)
print(a[:,1])
What will be the output?

Index Error
[2 12]
[10 12 14 16 18]
[2]

Answer 108

a = array([ 0, 2, 4, 6, 8, 10, 12, 14, 16, 18])

a.shape = array([[ 0, 2, 4, 6, 8], [10, 12, 14, 16, 18]])

a[:1] = [2, 12]

Question 109

Which search algorithm have you learned in class?

Answer 109

Sequential Search:
Starting at the first item in the list, we simply move from item to item, following the underlying sequential ordering until we either find what we are looking for or run out of items. If we run out of items, we have discovered that the item we were searching for was not present.

–> less efficient, particularly when target item is at the end of the collection or not present
(–> sorted collecton can be an improvement here (sorted sequential search))

Binary Search (list needs to be sorted):
The binary search algorithm starts by picking an item that divides the list into approximately two halves. We then compare this middle item with the target item, which will result in three possible conditions:

The middle item is indeed the target item.
The target item is less than the middle item.
The target item is greater than the middle item.

Question 110

Which sortin algorithm did you learn in class?

Answer 110

Bubble Sort:

Selection Sort:

Insertion Sort:

Question 111

What is Bubble Sort?

Answer 111

The underlying idea is to bubble up the larger items to the top, or the end of the collection and sink down the smaller items to the bottom, or the start of the collection. Upon completing one iteration of traversing through the entire collection, the next largest item will be in place (i.e. at its correct position).

Bubble Sort is regarded as one of the most inefficient sorting algorithms due to the total number of swaps (or re-ordering) that need to be performed in the inner loop of the algorithm. If the list is in reverse order, the number of swaps can be expensive in terms of computation.

Question 112

What is Selection Sort?

Answer 112

the Selection Sort algorithm only requires one swap at the end of each iteration having traversed through the collection. In each iteration, we attempt to find the next smallest item (or it could be the next largest item) by comparing each pair of adjacent items and place the smallest item (or the largest item) at the correct position at the end of the iteration. Note that we are still required to perform n-1 iterations like Bubble Sort if there are n items in the collection.

You may realise that both Bubble Sort and Selection Sort algorithms perform the same number of comparisons. However, Selection Sort is slightly more efficient than Bubble Sort in general as it reduces the number of swaps (re-ordering) to only one in each iteration.

Question 113

What is Insertion Sort?

Answer 113

The basic idea is to pick each of the items from the unsorted sublist and insert it into the correct position within the sorted portion; as such the ‘sorted’ sublist grows each time a new sorted item is correctly placed.

Comparison with Bubble sort and Selection sort:
The total number of comparisons and reordering (shifting) could be reduced in particular if the collection is almost sorted

Question 114

Which two methods are used for an analgorithm’s performance evaluation:

Answer 114

Time Complexity:
- The amount of time needed to complete an algorithm’s execution.
- Big O notation to describe the performance
- Worst Case:
linear in the length of the list for linear_search
must search the entire list and not find it
- Best Case:
constant for linear_search
first element in any list

Space Complexity:
The amount of memory space needed to complete an algorithm’s execution.

Question 115

Time complexity of linear search?

Answer 115

O(n)

Question 116

Time complexity of binary search?

Answer 116

O(log n)

Question 117

Time complexity of bubble sort, selection sort, insertion sort?

Answer 117

O(n^2)

Question 118

What is the definition of divide-and-conquer?

Answer 118

The technique of breaking down a problem into small manageable chunks of code.

Question 119

What are the key parts of devide-and-conquer?

Answer 119

Divide: the problem into smaller and simpler sub-problems of the original problem.

Conquer: the subproblems by solving them recursively using the same solution (function) until a base case has been reached –> has to converge to the base case

Combine: the solutions of the sub-problems to get the solution for the original problem.

Question 120

Are recursive functions only capable of solving the simplest case.?

Answer 120

True

Question 121

What are the three key requirements for recursive functions?

Answer 121

Base case: The recursive function must have a base case (i.e. the simplest form)

Convergence: The recursive function must be able to decompose the original problem into sub-problems; and must be converging toward the base case

Recursive case: The recursive function must call itself recursively to solve the sub-problems

Question 122

What will the following code print?

def f(x = 0, y = 1):
return x * y

print(f(1))

Answer 122

In the function call f(1), only one argument is given. This gets assigned to the parameter x, and the parameter y takes its default value 1.

Question 123

How would you write
def f(x):
return x - 1

in an anonymous function with lambda expression?

Answer 123

lambda x: x-1

def func(args):
return ret_val

lambda args: ret_val

Question 124

Create an anonymous function that takes a string and returns the last character in that string.

Answer 124

lambda string: string[-1])(“help”)

Question 125

Explain the map() function

Answer 125

The map() function takes in a function and a sequence, and returns a map object. The first argument (i.e., function) inputs each element of the second argument (i.e., sequence) and replaces each respective element with the value returned by the first input.

def triple(value):
return 3*value

def tripleStuff(a_list):
new_seq = map(triple, a_list)
return list(new_seq)

def quadrupleStuff(a_list):
new_seq = map(lambda value: 4*value, a_list)
return list(new_seq)

print(list(map((lambda value: 5*value), [1, 2, 3])))

Question 126

What is a filter?

Answer 126

Going through a list and keeping only those items that meet certain criteria is called a filter.

Question 127

filter_obj = filter(lambda num: num % 3 == 0, range(10))
print(list(filter_obj))

filter_obj = filter(lambda num: False, range(10))
print(list(filter_obj))

filter_obj = filter(lambda num: True, range(10))
print(list(filter_obj))

filter_obj = filter(lambda num: 0, range(10)) .
print(list(filter_obj))

filter_obj = filter(lambda num: 1, range(10))
print(list(filter_obj))

Answer 127

[0, 3, 6, 9]
[]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[] #0 evaluates to False
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] #1 evaluates to True