Python Part

Question 1

What does a condition evaluate to?

Answer 1

Boolean. True or False

Question 2

What does a break statement do?

Answer 2

Immediately exits whatever loop it is in, and skips the remaining expressions in the code block.

Question 3

In a for loop, there is an unbounded number of iterations that you don’t know. True or false?

Answer 3

False. You know the number of iterations in a for loop. In a while loop there is an unbounded number of iterations

Question 4

Which of the following are mutable:

a. Strings
b. Lists
c. Tuples

Answer 4

b. lists

Question 5

What can you use to slice a string?

Answer 5

string[start:stop:step]

Question 6

What is a docstring?

Answer 6

A docstring is a string literal specified in source code that is used, like a comment, to document a specific segment of code; so, basically just an explanation of what the outputs should be and what to expect from a function, just to make your code easier to read and understand in case you wanna use it somewhere else

You can access the docstring with help(functionname)

Question 7

Inside a function, you can access a variable defined outside. True or false?

Answer 7

True

Question 8

Inside a function, you can modify a variable defined outside (without global variables). True or false?

Answer 8

False

Question 9

What is a higher order function?

Answer 9

A higher-order function is a function that does at least one of the following:
takes one or more functions as arguments
returns a function as its result

Question 10

Define the scope of a variable.

Answer 10

The scope is mapping of names to objects

I don’t know why I put this in

Question 11

A return statement ends the execution of the function call and returns the result. True or false?

Answer 11

True

Question 12

What does “lists are mutable” mean?

Answer 12

It means that list elements can be changed.

Question 13

L.append(5). What does the dot do? (L is a list)

Not necessary append, but what does the dot between L and append mean

Answer 13

Lists are Python objects, everything in Python is an object. Objects have data. Objects have methods and functions. One can access this information by object_name.do_something ().

Question 14

To combine lists together you can use the + operator. True or false?

Answer 14

True. L1 = [1,2,3] and L2 = [4,5,6]. L1+L2 = [1,2,3,4,5,6]

You can also use L1.extend(L2)

Question 15

What does the method .pop on a list do?

Answer 15

It removes the element at the end of the list and returns the removed element.

Question 16

When you use L.remove(element), what happens? What if you have the same element two times? What if the element is not in the list?

Answer 16

It looks for the element and removes it. If the element occurs multiple times, it only removes the first occurrence. If the element is not in the list, it gives an error.

Question 17

What can you use to delete an element at a specific index in a list?

Answer 17

del(L[index])

Question 18

Assume s is a string. What do you use to convert it to a list containing every character from s?

Answer 18

list(s)

Question 19

What does s.split(“,”) do? s is a string

Answer 19

It is splitting a string on a character parameter. It splits on spaces if called without a parameter.

Question 20

Think of a list. What is the difference between sort() and sorted()

Answer 20

L = [1,4,3,1]
sorted(L) - returns the sorted list, does not mutate L
L.sort() - mutates L = [1,2,3,4]
L.reverse() - mutates L = [4,3,2,1]

Question 21

What do you use to get the absolute value of something?

Answer 21

abs()

Question 22

Tuples are immutable. True or false?

Answer 22

True.

Question 23

What is a tuple?

Answer 23

An ordered sequence of elements, in which you can mix the element types:
(2, “plant”, 3)

Question 24

When you set an alias to a list (i.e. you have a list called hot and you have some elements in it, and then you write warm = hot) and you append one element to one of the lists, does it append to the other one as well?

Answer 24

Yes. append() has a side effect, both lists warm and hot have the same object in memory.

You can solve this issue by cloning a list as follows:
warm = hot[:]

which means that you take all the elements from the hot list and you put them in warm, these two lists will have different objects in memory

The same thing happens with nested list!!!

Question 25

What is recursion?

Answer 25

A programming technique where a function calls itself.

Question 26

What is the first step in the process of writing a recursion?

Answer 26

1. You must have 1 or more base cases that are easy to solve
2. You must solve the same problem on some other input with the goal of simplifying the larger problem input

(sorry i put this question in, i dont know what i was thinking)

Question 27

What does a dictionary store?

Answer 27

It stores pairs of data. it has keys and values

Question 28

What methods can you use on dictionaries to iterate through the keys and values?

Answer 28

.keys() separately
.values() separately

.items() together

Question 29

A dictionary automatically stores keys in order. True or false?

Answer 29

False

Question 30

Values and keys can be duplicates in a dictionary. True or false?

Answer 30

False. Only values can be duplicates. Keys are always unique.

Question 31

A list is indexed by a range of numbers, while dictionaries are indexed by a set of unique keys. True or false?

Answer 31

True

Question 32

The order matters in the dictionary, but does not matter in a list. True or false?

Answer 32

False, the order does not matter in a dictionary because you have the unique keys to use as a lookup table, while for lists, the order matters

Question 33

What is the difference between classes and objects?

Answer 33

Classes and objects both have attributes and methods, but the difference is that a class is an abstract template, while an object is a concrete representation of a class.

Question 34

What is the difference between a method and an attribute?

Answer 34

A method is an attribute, but not all attributes are methods. For example, if we have the class

class MyClass(object):

class_name = 'My Class'

    def my_method(self):
        print('Hello World!')

This class has two attributes, class_name and my_method. But only my_method is a method. Methods are functions that belong to your object. There are additional hidden attributes present on all classes.

Question 35

What does every object have? (3 characteristics)

Answer 35

1. A type
2. An internal data representation (primitive or composite)
3. A set of procedures for interaction with the object

Question 36

What is the difference between primitive data types and composite data types?

Answer 36

Primitive data types are byte, short, int, bool, long, float, double, char…

Composite data types are the data types that can be constructed using the primitive data types and other composite types. Examples include lists, arrays, dictionaries…

Question 37

What are objects?

Answer 37

Objects are data abstractions that capture:

1. an internal representation - through data attributes
2. an interface for interacting with the objects - through methods

Question 38

What are some advantages of OOP (object-oriented programming)?

Answer 38

One can bundle data into packages together with procedures that work on them through well-defined interfaces

“Divide-and-conquer” development = implement and test behavior of each class separately; increases modularity and reduces complexity

Classes make it easy to reuse code or for subclasses to inherit some behavior

Question 39

What are attributes of a class?

Answer 39

Attributes are data and procedures that belong to the class.

Data attributes - think of data as other objects that make up the class (e.g., a coordinate is made up of two numbers)

Methods (procedural attributes) - think of methods as functions that only work with this class

Question 40

What is __init__?

Answer 40

A special method to initialize some data attributes. It allows us to kickstart the object with some specific attributes

Question 41

Getter and setter method. Click

Answer 41

No idea. write more when you arrive here

Question 42

When do the following errors appear?

a. IndexError
b. TypeError
c. NameError
d. SyntaxError

Answer 42

a. IndexError appears when trying to access beyond list limits
b. TypeError appears when trying to convert to an inappropriate type, or mixing types without coercion
c. NameError appears when referencing a non-existing variable
d. SyntaxError appears when Python can’t parse the program because of some syntax mistake in the code

Question 43

How does try & except handling work?

Answer 43

Exceptions raised by any statement in the body of “try” are handled by the “except” statement and the execution continues with the body of the “except” statement.

Question 44

How does “raise” exception handing work?

Answer 44

The program can raise an exception when it is unable to produce a result consistent with the function’s specifications

Question 45

How do assertions work in Python?

Answer 45

When you want to be sure that the assumptions on the state of computations are as expected, use an “assert” statement to raise an AssertionError exception if assumptions are not met.

This is a good practice of defensive programming.

e.g.,
assert len(grades) != 0, "not good"

Question 46

What is the goal of assertions?

Answer 46

To spot bugs as soon as they are introduced and make clear where they happened.

Question 47

NumPy arrays comprise elements of a single data type. True or false?

Answer 47

True

Question 48

What is an array?

Answer 48

An array is a data structure consisting of a collection of elements, each identified by at least one array or index key. An array is stored such that the position of each element can be computed from its index tuple.

Question 49

What do these different methods do?

a. np.arrange(10)
b. np.zeros((2,2))
c. np.ones((2,2))
d. np.empty((1,3)
e. np.eye(3)
f. np.diag([1,2,3,4])
g. np.linspace(0, 1, 5)

Answer 49

They create different arrays, other than explicitly stating a list of values (np.array([1,2,3]))

If unsure about what one does, Google it, or check Lecture 5.

Question 50

Remember that you have to make a copy of a list to be able to apply some methods on one of them without affecting the other one? Good. Do you know if that is the case with arrays as well?

Answer 50

Yes, the arrays work the same way. Simple assignments do not make copies of arrays.

Question 51

When you have two arrays, a & b, and you compute a + b, the arrays are appended to each other, just like lists. True or false?

Answer 51

False, unlike lists c = a + b will compute the sum of the corresponding entries in the arrays. This is an example of a universal function (or ufunc) of NumPy.

Question 52

If we want to transfer a numpy array into another dimension, we can refer to their axis.

In an array like the following:
0 1 2 3 4
5 6 7 8 9
10 11 12 13 14

What does the following code return?

a. array.sum(axis = 0)
b. array.sum(axis = 1)

Answer 52

axis = 1 reduces into the first dimension; which means that the program does something with the rows

array.sum(axis = 1) returns
[10 , 35 , 60], which is the sum row-wise

axis = 0 reduces into the zero dimension; which means that the program does something with the columns

array.sum(axis = 0) returns
[15 , 18 , 21 , 24 , 27], which is the sum column-wise

Question 53

What do you find out from array.shape method?

Answer 53

The number of elements in the array

dimensions

Question 54

What is pandas?

Answer 54

Pandas is a rich relational data tool built on top of NumPy

Question 55

What is a data frame?

Answer 55

some characteristics:
NumPy array-like

Each column can have a different type

Row and column indexes

Size mutable: insert and delete columns

Question 56

How can you access a column/s through square brackets in a data frame?

Answer 56

e.g.,

brics[[“country”, “capital”]]

dataframe_name[[column_1, column_2]]

Question 57

What is the difference between the methods .loc and .iloc when locating some stuff in a pandas data frame?

Answer 57

loc gets rows (or columns) with particular labels from the index

iloc gets rows (or columns) at particular positions in the index (so it only takes integers).