Python Moodle Flashcards

Question

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 1

+ 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.

Answer 2

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

Answer 3

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

Answer 4

The split method breaks a string into a **list** of words. --------------------- ['The', 'rain', 'in', 'Spain...'] By default, any number of whitespace characters is considered a word boundary. --------------------- ['The r', 'n in Sp', 'n...']

Answer 5

The join mehtod is the inverse of the split method. --------------------- red;blue;green ['red', 'blue', 'green'] red***blue***green redbluegreen

Answer 6

12 --> whitespace is a character

Answer 7

3 [n:m] --> n wird mitgezählt, m nicht

Answer 8

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.

Answer 9

2 There is a difference between "we" and "We" which means there are only two in the string --> case sensitive

Answer 10

G o S p o t G o

Answer 11

starts at 0 and goes up to but not including n. range(3) --> [0,1,2]

Answer 12

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

Answer 13

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

Answer 14

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

Answer 15

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

Answer 16

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.

Answer 17

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".

Answer 18

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)

Answer 19

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.

Answer 20

primitive data types abstract data types user-defined data types

Answer 21

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

Answer 22

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.

Answer 23

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

Answer 24

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)

Answer 25

Error, strings are immutable.

Answer 26

[4,2,8,6,5]

Answer 27

Error, you cannot concatenate a list with an integer.

Answer 28

2.3 2.35 2.3456700

Answer 29

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

Answer 30

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

Answer 31

- 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

Answer 32

- 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

Answer 33

x.keys() --> returns a view of the keys in the dictionary x.values() --> returns a view of the values in the dictionary x.items --> returns a view of the key-value pairs 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

Answer 34

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

Answer 35

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}

Answer 36

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

Answer 37

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

Answer 38

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

Answer 39

instantiation

Answer 40

- 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.

Answer 41

Define the part of the program where a variable is accessible

Answer 42

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

Answer 43

Can be accessed throughout the entire program Exists until the execution of the program terminated

Answer 44

Can only be accessed within the function it was defined Exists until the function exists

Answer 45

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

Answer 46

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.

Answer 47

In OOP of Python, function is known by "method".

Answer 48

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

Answer 49

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

Answer 50

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

Answer 51

- 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

Answer 52

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.

Answer 53

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

Answer 54

Determines the class name of any value. For example: >>> help() usually gives information of the class on any built-in type or function.

Answer 55

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

Answer 56

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

Answer 57

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

Answer 58

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

Answer 59

With mode 'w' and 'a'

Answer 60

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

Answer 61

- valid cases - invalid cases - boundary cases.

Answer 62

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()

Answer 63

unittest is a package to automate testing

Answer 64

- 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

Answer 65

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

Answer 66

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

Answer 67

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

Answer 68

check if a==b assertEqual(first, second, msg=None)

Answer 69

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()

Answer 70

result = string + int --> TypeError

Answer 71

.set_x() doesn't exist --> AttributeError

Answer 72

Import Error

Answer 73

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

Answer 74

No ouput. assert x>y returns True and no other print ouput --> no ouput if x

Answer 75

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

Answer 76

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

Answer 77

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.

Answer 78

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.

Answer 79

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" print(re.sub(pattern, replace_word, text)) ------------------------- python is fun. python is fast, easy to learn, and awesome.

Answer 80

[Pp]: it creates the group of characters that we want to match; in our case, we want to find [Pp] '.*?': it tries to match any number of characters and stops when the next character in the regex is found [Nn]: it is similar to the "[Pp] group", which tries to check the "n" or "N"

Answer 81

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

Answer 82

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]

Answer 83

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.

Answer 84

Bubble Sort: Selection Sort: Insertion Sort:

Answer 85

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.

Answer 86

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.

Answer 87

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

Answer 88

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.

Answer 89

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

Answer 90

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.

Answer 91

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

Answer 92

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.

Answer 93

lambda x: x-1 --------------------------- def func(args): return ret_val lambda args: ret_val

Answer 94

lambda string: string[-1])("help")

Answer 95

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])))

Answer 96

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

Answer 97

[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